OPTICAL  TRUTHS. 


ILLUSTRATED. 


By  CHARLES  McCORMICK,  M.  D., 

President  McCormick  Optical  College, 
CHICAGO. 


Published  by 
McCORMICK  OPTICAL  COLLEGE, 
J     84  Adams  Street,  Chicago. 


OPTOMETRY  LIBRARY 


Copyright  1898,  by 
Charles  McCormick. 


The  Cambridge  Press,  Marsh  &  Grant  Ptg.  Co. 
359-361  Dearborn  St.,  Chicago. 


off 01^ 


TO   THE 

SWEET  SPIRIT, 

WHO   HAS   BEEN,    IS,    AND   EVER    SHALL    BE 

MY  INSPIRATION, 

THIS   BOOK 
IS 

DEDICATED. 


5i>o5^ 


CONTENTS. 


Abbreviations, 9 

Introduction, 11 

PART  I. 

CHAPTER  I.  —  The   Laws  of  Refraction   Stripped  of  Com- 
plications,         17 

CHAPTER  II.  —  Measurement  of  Lenses  and  Prescription  Writ- 
ing,   29 

CHAPTER   111.— Refraction   of  the    Dioptric  System    of    the 

Eye, 39 

CHAPTER  IV.— The  "Fogging"  Method   of  Measuring  Errors 

of  Refraction, 5  5 

CHAPTER  V. —  Machine  Tests— Objective  and  Subjective  Meth- 
ods Compared, 67 

CHAPTER  VI.— The    Clinical    Value    of    Perfectly    Adjusted 

Frames  and  Lenses,         ....  75 


CONTENTS— Continued. 

PART  n. 

CHAPTER  I.  —  Exposing    Ophthalmological  Charlatans   and 

their  Practices, 79 

CHAPTER  II.  —  Operations,     Medicines    and    Prisms,    Three 

Great  Ophthalmological  Blunders,  .        .  91 

CHAPTER  III. — Affections  of  the   Eyes,    Commonly    Called 

Disease, 103 

CHAPTER  IV. — Anatomy  and  Physiology  of  the  Eye  and  its 

Appendages, 117 

CHAPTER  V. —  Mydriatics  and  Myotics — Drugs  which  Act  on 

the  Accommodation,  .        .        12^ 

CHAPTER  VI. — Color-Blindness,     and   a    Comparison  of  the 

Tests  Therefor, 125 


APPENDIX— A  Quiz  Compend,  Embracing  the  Principal  Points 

of  Practice, 133 

GLOSSARY — Comprising  a  List  of  Optical  Terms  and  Their 

Meaning, 147 


ABBREVIATIONS. 


ACC 

.     Accommodative  power 

AM. 

Ametropia. 

AS. 

Astigmatism. 

C. 

Cornea. 

cc. 

or  CVE.     Concave. 

Cm. 

Centimetre. 

Cx. 

or  Cvx.     Convex. 

Cyl 

,     Cylinder. 

D. 

Dioptre. 

E. 

Emmetropia. 

F. 

Formula, 

H. 

Hyperopia. 

L. 

Left. 

M. 

Myopia. 

Mm 

.     Millimetre. 

O.  D.     Right  eye  {ocular  dexter). 
O.  S.     Left  eye  {ocular  septimus). 
O.  U.     Both  eyes  {ocular  unose). 
Pec.  or  PCVE.     Periscopic  concave. 
PCX.  or  Pcvx.     Periscopic  convex. 
Pp.     Punctum  Proximum  (near  point). 
PR.     Punctum  Remotum  (far  point). 
R.     Right. 
Sph.     Spherical. 
V.     Vision,  or  acuteness  of  vision. 

Plus. 

Minus. 

Equal  to. 

Combined  with. 

Combined  with  at  right  angles. 

Infinity,  twenty  feet  away. 


INTRODUCTION. 

In  the  practice  of  ophthalmology  one  of  the  essentials  is  a  gener- 
al knowledge  of  the  nervous  system,  what  it  is,  whence  it  cometh, 
and  whither  it  goeth. 

It  is  simply  a  complete  telegraph  system,  intimately  connecting 
every  portion  of  the  anatomy. 

In  structure  it  is  a  series  of  tubular  membranes  containing  in  a 
minute  and  continuous  stream,  matter  identical  with  the  brain  sub- 
stance, through  which  electrical  energy  is  transmitted. 

This  energy  is  of  two  kinds,  galvanic  and  faradic.  The  first  is 
generated  by  the  digestive  organs,  and  is  constant;  the  second,  is  an 
intermittent  current  generated  by  molecular  friction  throughout  the 
body. 

The  nervous  system  is  divided  into  two  classes,  the  cerebro- 
spinal or  animal,  and  the  sympathetic  or  organic. 

There  are  two  currents  of  nerve  force:  The  afferent,  from  the 
peripheral  parts  to  the  nerve  centers,  and  the  efferent,  from  the  nerve 
centers  to  the  peripheral  parts. 

The  brain  is  the  chief  nerve  center.  All  force  is  sent  there,  and 
thence  distributed  in  every  direction  and  in  such  proportions  as  condi- 
tions require.  To  do  this  the  brain  gives  off  twelve  pairs  of  cranial 
nerves  and  the  spinal  cord,  the  latter  being  the  grand  trunk  line  which 
supplies  the  minor  centers,  or  plexuses,  in  the  body. 


12  INTRODUCTION. 

There  are  two  functions  devolving  upon  the  nerves,  motion  and 
sensation. 

The  cranial  nerves  are  numbered  and  named  as  follows: 
1     Olfactory,  nerves  of  smell. 
11     Optic,  nerves  of  sight. 

III  Motor  Oculi,  motor  nerves,  which  supply  all  the  muscles 

of  the  eyes,  save  two. 

IV  Patheticus  or  Trochlear,  motor  nerves,  which  supply  the 

superior  oblique  muscles  of  the  eyes. 

V  Trigeminus,  nerves  of  sensation  and  motion,  having  three 

main  branches,  one  to  the  eyes,  and  two  to  the  upper 
and  lower  jaws. 

VI  Ahducens,  motor  nerves,  which  supply  the  external  recti 

muscles  of  the  eyes. 
Vll     Facial  or  Portio  Dura,  motor  nerves  of  face,  ear,  palate 

and  tongue. 
VIII    z/iuditory,  nerves  of  hearing. 
IX    Glosso- Pharyngeal,  nerves  of  taste. 
X    Pneumogastric,  nerves  of   motion  and   sensation,   which 
supply  the  lungs,  stomach,  heart  and  their  accessories. 
XI     Spinal  Accessory,  to  the  Tenth. 
XII    Hypo-glossal,  nerves  of  motion  of  the  tongue. 
The  nerves  given  off  from  the  spinal  cord  number  3 1  pairs,  and 
they  form  five  principal  centers  or  plexuses,  as  follows,  in  the  order 
of  vertebral  subdivisions:     Cervical,  8  pairs;     Dorsal,  12;     Lumbar, 
5;    Sacral,  5;    Coccygeal,  1. 

Each  nerve  contains  both  animal  and  organic  qualities,  so  that 
we  have  not  only  the  power  of  motion  and  sensation,  but  also  the 


INTRODUCTION.  t3 

sympathetic  relation  between  all  parts  which  is  absolutely  necessary  to 
health  and  control  of  functions. 

In  normal  physiological  conditions  the  distribution  of  nerve 
force  -S  proportional  to  the  capacity  for  supply,  and  Nature  has  so 
arranged  that  the  brain  contains  a  reserve  stock  for  emergencies. 
Were  it  not  for  this  wise  provision  the  suspension  or  decrease  in 
capacity  of  the  source  of  supply  would,  surely  and  speedily,  result  in 
death. 

In  youth  the  quantity  of  reserve  force,  as  well  as  the  capacity  for 
supply  is  greater,  hence  the  more  speedy  recovery  from  injuries  and 
ills.  Extraordinary  drain  upon  the  nerve  supply  can  be  endured 
without  discomfort,  because  of  these  conditions.  When,  however  the 
reserve  supply  is  exhausted,  the  demand  is  made  directly  upon  the 
capacity  of  the  machinery  and  trouble  follows. 

Any  abnormal  physiological  condition,  or  functional  demand 
which  requires  more  than  the  normal  proportion  of  nerve  force  in 
one  direction,  will  have  evil  etfects  upon  other  functions  as  soon  as 
the  reserve  is  reduced  below  the  safety  line.  One  of  these  is  the 
intense  thought  associated  with  grief,  joy,  fear,  anger  and  other  emo- 
tions, because  the  demand  is  directly  upon  the  chief  source  of 
supply. 

In  this  connection  it  is  interesting  to  note  by  experiment,  the  elTect 
of  thought  upon  the  various  functions.  The  phenomena  of  blushing, 
turning  pale,  etc.,  are  illustrations  of  the  influence  of  thought  upon 
the  nerves  which  control  the  circulation  of  blood. 

The  influence  of  the  mind  upon  the  body  is  being  recognized  by 
the  medical  colleges  of  today,  and  psychology  is  one  of  the  special 


14  INTRODUCTION. 

branches  taught. .  The  Faith  Healers  find  the  basis  for  their  work  in 
the  same  proposition,  coupled  with  a  fanatical  belief  that  they  are 
especially  endowed  by  God. 

Each  case  which  presents  itself  to  the  ophthalmologist  has  indi- 
vidual peculiarities,  and  only  a  thorough  knowledge  of  elementary 
principles  of  anatomy,  physiology,  neurology,  physics,  psychology 
and  mathematics  will  enable  the  practitioner  to  meet  them  with  credit 
to  himself  and  comfort  to  his  patients.  He  must  also  cultivate  his 
common  sense,  and  look  for  the  simplest  way  out  of  any  difficulties 
which  may  arise. 

In  the  following  pages  the  author  endeavors  to  give  information, 
accompanied  by  practical  reasons  for  each  proposition,  and  trusts  it 
will  be  of  service  to  all  into  whose  hands  it  may  come. 

The  cuts,  excepting  those  of  instruments,  were  all  made  expressly 
for  this  work,  and  are  correct  according  to  the  laws  which  they  illus- 
trate. 

The  colored  plates  were  drawn  by  Professor  Frank  Rumble,  of 
McCormick  Optical  College.  Those  representing  retina  were  made 
from  ophthalmoscopic  observations. 


PART  I. 


CHAPTER  I. 
The  Laws  of  Refraction  Stripped  of  Complications, 


^Definition — Refraction  is  the  deviation  in  its  course  a  ray  of 
light  suffers  in  passing  obhquely  from  one  transparent  medium  to 
another  of  different  density. 

The  amount  of  refraction  is  governed  by  the  angle  of  incidence 
and  the  density  of  the  medium,  and  it  is  measured  according  to  nat- 
ural laws. 

Air  is  taken  as  the  standard  of  measurement  of  refraction,  and  is, 
therefore,  designated  by  the  unit,  1,  because  a  ray  in  passing  from 
one  space  to  another,  in  air,  would  suffer  no  change  in  its  course,  and 
angles  formed  by  it  with  vertical  lines  would  always  be  of  equal 
size. 


18 


OPTICAL  TRUTHS. 


Let  the  line  starting  from  R,  in  the  cut,  represent  a  ray.  After 
crossing  the  line  c^  'B  at  the  line  C  D  it  continues  on  its  course  toward 
5  without  deviation,  consequently  angles  1  and  2  are  of  equal  size. 

M 


The  cut  above  shows  what  would  occur  if  a  ray  from  R  should 
come  in  contact  with  a  body  of  water  at  the  point  where  it  crosses 
the  line  A  B.  Its  course  would  be  changed,  for  the  reason  that  its 
movement  is  swifter  in  the  rarer  medium,  and,  its  lower  edge,  meet- 
ing the  obstruction  first,  would  be  retarded  in  its  progress,  while  the 
upper  edge  would  continue  its  speed,  thus  gaining  on  the  other,  so 
that  the  course  of  the  ray  through  the  denser  medium  would  be 
toward  T>  instead  of  in  the  direction  C.  As  it  passes  obliquely 
through  the  water,  it  will  be  seen  the  lower  edge  would  be  released 
first,  and,  renewing  its  original  pace,  would  gain  on  the  other  edge, 


LAWS  OF  REFRACTION.  19 

recovering  what  it  had  lost  at  the  first  surface,  and  would  pass  toward 
E,  parallel  to,  but  not  on  the  line  of  its  original  course. 

From  the  amount  of  deviation  as  shown  by  the  comparative  pro- 
portions of  the  angles  formed  in  the  two  mediums,  we  learn  the  pro- 
portionate rates  of  speed  at  which  a  ray  will  move  through  various 
mediums.  Air,  being  the  rarest  is  taken  as  the  standard.  All  other 
mediums  are  compared  with  it,  and  the  expressed  ratio  is  called  Index 
of  Refraction.  The  proportion  of  the  angles  in  air  and  water  is  as  4 
is  to  3,  hence,  the  index  of  water  is  1.33,  because  it  would  take  1  '3  of 
its  angle  to  equal  the  angle  1  in  the  air.  The  proportion  of  air  and 
glass  is  as  3  to  2,  so  the  index  of  glass  is  1.50.  The  diamond  has  the 
greatest  refracting  power,  the  proportion  of  air  and  diamond  being  5 
to  2,  therefore  its  index  is  2,50. 

According  to  its  index  of  refraction  water  would  cause  the  ray 
to  change  its  course  so  that  the  length  of  the  angle  formed  by  the  ray 
and  the  vertical  line  at  the  lower  surface  (2  in  the  cut)  would  be  in 
proportion  to  that  formed  by  the  ray  and  vertical  line  at  the  same  dis- 
tance (1)  above  the  first  surface,  as  1  is  to  1.33. 

The  same  law  applies  in  passing  from  the  dense  to  the  rare  med- 
ium below,  the  angle  at  3  being  1.33  times  as  great  as  that  at  4. 

A  ray  is  called  incident  before  it  enters  the  denser  medium, 
refracted  during  its  passage  and  emergent  after  it  has  passed. 

The  angle  formed  by  the  incident  ray  and  the  vertical  line  A  B, 
is  called  the  angle  of  incidence;  that  formed  by  the  refracted  ray  and 
the  same  line,  the  angle  of  refraction;  and  that  formed  by  the  emer- 
gent ray  and  the  line  x  y,  the  angle  of  emergence. 

A  ray,  in  making  a  passage  as  illustrated,  suffers  the  loss  of  a 
portion  by  reflection  at  the  first  surface,  and  it  is  a  law  of  optics  that 


20  OPTICAL  TRUTHS. 

the  angle  of  reflection  always  equals  the  angle  of  incidence,  hence  it 
follows  that  the  retlected  portion  would  pass  toward  Fforming  another 
angle  with  the  line  A  B,  called  the  angle  of  reflection. 

It  will  be  observed  that  the  angles  of  emergence  and  incidence 
are  of  equal  size;  therefore,  a  ray  starting  at  £,  would  pursue  the  same 
course,  and  '7^  would  be  the  emergent  ray,  which  fact  gives  us  another 
law,  viz. :  The  course  of  returning  rays  is  always  upon  the  same  lines 
by  which  they  enter. 

If  an  incident  ray  forms  an  angle  with  the  perpendicular  greater 
than  about  fifty  degrees  it  will  suffer  total  reflection.  This  is  called 
the  limit  angle. 

It  is  well  known  that  natural  light  is  composed  by  a  combination 
of  all  the  spectral  colors.  The  passage  of  a  ray  through  any  medium 
which  reduces  its  original  speed  causes  a  derangement  of  its  compo- 
nents, the  medium  absorbs  a  portion,  while  it  also  makes  an  attempt 
to  disperse  it  into  its  elementary  colors;  so,  any  ray,  in  passing  from 
one  transparent  medium  to  another  of  different  density,  suffers  from 
reflection,  dispersion  and  absorption;  and,  if  it  passes  obliquely,  it 
also  suffers  refraction. 

Wtrt  it  not  for  reflection  we  could  not  see  objects  which  are  not 
in  themselves  luminous;  and,  were  it  not  for  dispersion  and  absorp- 
tion the  power  of  the  reflected  light  would  be  so  great  as  to  be  painful 
to  the  nerves  of  vision. 


LAWS  OF  REFRACTION.  21 

This  figure  illustrates  the  dispersive  power  of  glass,  with  the 
ray  passing  from  A  toward  %  at  such  an  angle  of  incidence  that 
the  greatest  possible  effect  from  the  prism,  C,  is  shown. 

It  is  a  curious  fact  that/////  glass,  with  a  refractive  power  about 
equal  to,  has  twice  as  much  dispersive  power  as  the  croiLm  glass  from 
which  spectacle  lenses  are  made.  It  was  the  discovery  of  this  which 
enabled  the  makers  of  the  finer  grades  of  optical  goods,  such  as  mi- 
croscopes, etc.,  to  attain  their  present  approximate  to  perfection.  Pre- 
viously two  factors  interfered  with  the  successful  use  of  lenses  with 
more  than  about  twenty-five  diameters  magnifying  power.  These 
were  chromatic  and  spherical  aberration .  The  first  is  the  effect  of 
the  dispersive  power,  and  is  the  term  employed  when  the  image  is 
fringed  with  color;  the  second  is  the  result  of  imperfect  refraction, 
the  edge  rays  in  high  power  lenses  violating  the  law  and  coming  to  a 
focus  just  a  little  sooner  than  those  which  pass  the  main  body  of  the 
lens,  thus  causing  an  indistinct  image.  The  discovery  referred  to  has 
enabled  the  manufacturers  to  overcome  both  of  these  factors  and 
thus  utilize  the  whole  field  of  the  lens.  Formerly  it  was  necessary  to 
rough-grind  the  marginal  field  to  even  partially  overcome  the  difff- 
culties. 


This  cut  shows  the  dispersion  of  the  ray  from  '7^  in  the  crown 
glass,  C,  and  the  contrary  effect  in  the  flint  glass,  F,  which  reunites 


22 


OPTICAL  TRUTHS. 


the  parts,  and  the  emergent  ray  becomes  white  again.  The  tlint 
glass,  ^,  being  half  as  strong  in  refractive  power  as  the  crown,  6,  and 
of  the  same  dispersive  power,  the  result  is  a  refractive  power  of  3 
in  the  combination,  without  any  dispersion.  It  is  upon  this  principle 
that  achromatic  and  aplanatic  lenses  are  made.  The  first  means  the 
chromatic  aberration  is  corrected,  and  the  second  is  a  lens  in  which  all 
faults  are  corrected. 


\ 

\ 

c 

/ 

\ 

/      iMiv 

•^ r=:^   _ :-  ^^ 

./ 

Ei" 

~—  jETcus^-^- 

//f 

JJi? 

r  D 

This  figure  illustrates  refraction  by  glass.  A  ray  from  C  upon 
meeting  the  surface  of  the  denser  medium  would  be  refracted  and 
take  the  course  toward  T),  forming  an  angle  of  refraction  in  propor- 
tion to  the  angle  of  incidence  as  1  is  to  t.50.  At  the  other  surface  it 
would  again  suffer  refraction  and  take  the  direction  F. 

Reference  to  the  illustrations  shows  that  rays  of  light  always 
move  in  straight  lines.  There  are  breaks  but  no  bends.  It  will  be 
seen,  also,  that  in  passing  from 'the  rare  to  the  denser  medium  the 


LAWS  OF  REFRACTION. 


23 


ray  is  broken  toward  the  perpendicular  to  the  surface,  and  in  passing 
from  the  dense  to  the  rarer  medium  it  is  broken  from  the  perpen- 
dicular. 

^  /d      ' 

/  ^ 
I 
I 


I  \ 

This  illustration  demonstrates  the  effect  upon  a  ray  passing  a 

prism.  Consider  one  surface  at  a  time.  The  line  projected  from  A, 
upon  meeting  the  first  surface  would  be  broken  and  follow  the  line 
drawn  through  the  denser  medium  to  the  second  surface,  which  it 
would  meet  at  a  different  angle,  the  result  of  which  would  be  a  sec- 
ond break  and  the  final  course  taken  to  "S.  The  dotted  lines  are 
drawn  to  enable  the  measurements  to  be  taken  correctly,  according 
to  the  index  of  refraction,  lines  a  and  h  representing  the  perpendic- 
ulars to  the  respective  surfaces,  and  the  lines  c  c  and  d  d  the  distances 
from  the  surfaces  at  which  the  measurements  were  taken. 

Law — Rays  of  light  in  passing  a  prism  are  always  broken  toward 
the  base  line . 

An  eye  at  A  would  see  an  object  placed  at  "B  as  if  it  were 
located  at  C.  This  is  called  the  virtual  or  imaginary  image,  and  it  is 
always  seen  at  a  point  nearer  the  apex  of  the  prism  than  the  object 
is  really  situated.  This  is  the  reason  convex  lenses  magnify,  and 
concave  minify  objects  seen  through  them. 


24  OPTICAL  TRUTHS. 

Now  if  we  should  take  another  prism  and  place  it  with  its  base 
abutting  the  base  of  the  first  one,  we  would  have  this: 


Project  parallel  rays  through  it  and  they  will  meet  at  points 
along  the  base  line  or  axis  as  it  is  now  called.  Here  we  have  the 
principle  upon  which  convex  (+)  lenses  are  formed. 

If  we  place  the  prisms  with  their  apices  toward  the  axial  line  the 
effect  would  be  just  opposite,  showing  the  principle  of  concave  ( — ) 
lenses,  thus: 


Observe  that  in  both  preceding  illustrations  the  central  line 
passes  through  without  refraction.  This  is  because  it  meets  the  sur- 
faces at  a  perpendicular.  It  is  well  to  remember  that,  referring  to 
lenses  of  all  kinds,  the  word  ''axis"  means  without  refractive  power. 

Note,  in  the  convex  cut,  that  while  parallel  rays  meet  on  the  axis 
after  passing  the  prisms,  they  do  not  meet  at  a  point  common  to  all. 
In  order  to  utilize  the  principles  of  refraction  for  optical  purposes  it 
is  necessary  to  grind  the  surfaces  of  the  prisms  so  that  they  will  be 
curved  instead  of  plane,  when  we  have  the  effect  of  a  multitude  of 
prisms,  of  different  angles,  and  parallel  rays  passing  them  will  be 
converged  to  a  single  point  on  the  axis,  no  matter  if  they  are  at  dif- 
ferent distances  from  the  axial  line  before  entering,  as  the  following 
drawing  shows: 


LAWS  OF  REFRACTION. 


25 


The  fact  that  the  curvature  of  either  surface  would,  if  continued, 
form  a  perfect  sphere,  caused  the  name  spherical  to  be  given  such 
lenses.  They  may  be  either  convex  or  concave,  and  each  class  is  sub- 
ject to  three  forms  of  construction,  thus: 


1,  Piano-Convex; 


I 

4  5 

Bi-Convex;    3,  Periscopic  Convex;      4,  Piano-Concave; 
5,  Bi-Concave;     6,  Periscopic  Concave. 

kixut  nodal  point  is  the  center  of  curvature;  but,  the  nodal 
points  of  a  lens  are  located  upon  the  axis  in  the  following  manner: 


26  OPTICAL  TRUTHS. 

A  ray  starting  from  7^  towards  /,  on  the  axis,  would  be  refracted 
and  cross  the  axis  as  shown  in  the  cut,  and  at  the  other  surface 
would  be  refracted  again,  taking  the  course  in  line  with  point  2  on  the 
axis.  The  points  /  and  2  are  designated  as  the  nodal  points  of  the 
lens,  and  the  point  between  them,  where  the  refracted  ray  crossed  the 
axis  is  the  optical  center  of  the  lens.  All  rays  which  cross  the  axis 
at  or  between  the  points  /  and  2  are  called  secondary  axial  rays.  As 
the  deviation  of  such  rays  is  very  slight  in  thin  lenses,  such  as  specta- 
cles, it  is  ignored,  and  in  drawings  all  are  passed  straight  through  the 
optical  center.  The  rule,  then,  is:  The  nodal  points  are  those  points 
upon  the  axis  where  secondary  axial  rays  would  cross  did  they  not 
suffer  refraction;  and  the  optical  center  is  the  point  on  the  axis  where 
the  refracted  secondary  rays  actually  cross. 

There  is  another  class  of  lenses  in  which  the  prisms  are  ar- 
ranged bases  in  for  convex  and  bases  out  for  concave,  but,  instead  of 
being  arranged  around  a  central  point,  as  in  the  sphericals,  they  are 
placed  on  either  side  of  a  line  drawn  from  edge  to  edge,  and  all  rays 
passing  through  the  lens  on  that  line  do  so  without  refraction.  This 
line  is  called  its  axis.  The  full  measure  of  power  of  such  lenses  is 
always  on  the  meridian  at  right  angles  to  the  axis.  The  curvatures 
of  these  lenses  would,  if  continued,  form  cylinders,  hence  they  are 
called  cylindricals.  They  are  made  only  in  the  forms  plano-convex 
and  plano-concave,  because  of  the  frequent  necessity  of  combining 
them  with  sphericals,  making  what  are  called  sphero-cylinders,  or 
compound  lenses,  in  which  there  is  refractive  power  in  all  meridians, 
but  in  the  two  principal  ones,  viz. :  on  the  meridian  where  the  axis 
is,  and  the  one  at  right  angles  to  it,  there  is,  respectively,  the  min- 
imum and  maximum  power. 


LAWS  OF  REFRACTION. 


27 


Convex  Cylinder.  Concave  Cylinder. 

The  following  figure  illustrates  the  chief  points  to  be  remem- 
bered in  determining  how  and  where  images  are  formed  by  conve  x 
spherical  lenses.  The  line  from  A  to  B  is  called  the  principal  axis  of 
the  lens,  (6),  because  it  passes  through  the  center  of  curvature  of 
both  surfaces  and  the  ray  which  follows  this  line  is  not  refracted;  also, 
because  it  must  be  distinguished  from  the  secondary  axes,  two  of 
which  are  shown  by  the  lines  e  F  and  G  H.  All  rays  which  cross 
the  principal  axis  at  the  optical  center  of  a  lens  are  secondary  axial 
rays. 

c  ^  c 

r 


All  rays  which  do  not  pass  through  a  lens  on  the  line  of  its 
principal  axis  sutTer  refraction,  but,  as  has  been  stated,  the  deviation 
in  their  course  of  the  secondary  axial  rays  is  so  slight  that  it  is  not 
considered.  The  points  at  2  and  9  are  called  the  principal  focal 
points  because  rays  which  come  from  the  opposite  side  of  the  lens, 
parallel  to  the  principal  axis,  would  focus  at  those  points,  which  are 


28  OPTICAL  TRUTHS. 

immovable.  The  lines  c  c  are  called  the  principal  focal  planes  be- 
cause they  correspond  to  the  principal  focal  points.  The  dotted  lines 
forming  the  diamond-shaped  figures  extending  from  e  io  F  and  Gto  H 
and  the  black  lines  from  /i  io  B  are  called  the  edge  rays.  By  noting 
how  they  converge  to  their  several  axes,  forming  points  after  passing 
the  lens,  the  manner  in  which  images  are  formed,  and  the  reason 
they  are  reversed,  will  be  seen.  Rays  from  any  point  on  the  object 
G  e,  will  be  focused  at  a  point  on  the  other  side  of  the  lens  on  the 
plane  F  H,  and  the  point  will  be  in  line  with  the  first  point  and  the  op- 
tical center  of  the  lens.  The  point  upon  the  principal  axis  where  the 
object  is  placed  is  the  first  conjugate  focal  point,  and  the  correspond- 
ing point  on  the  other  side  of  the  lens,  where  the  image  is  formed,  is 
the  second  conjugate  focal  point,  and  the  distances  between  each  of 
those  points  and  the  lens  are,  respectively,  the  Jirst  and  second  conju- 
gate focal  distances.  A  rule  to  locate  where  images  will  be  formed  is 
to  multiply  the  first  conjugate  focal  distance  by  the  focal  length  of  the 
lens  and  divide  the  product  by  the  difference  between  the  two  first  fig- 
ures; the  result  will  be  the  second  conjugate  focal  distance,  which,  in 
+  lenses  is  always  on  the  opposite  side  of  the  lens.  The  word  "con- 
jugate" means  "yoked  together,"  and  it  is  applied  to  the  points  de- 
scribed because  they  are  movable,  the  position  of  the  second  being 
always  dependent  upon  the  first.  In  the  cut  the  object  is  placed  at 
twice  the  focal  length  of  the  lens  and  its  image  is  formed  at  the  same 
distance  on  the  other  side,  and  is  of  the  same  size.  Move  the  object 
farther  away,  and  the  image  will  be  formed  closer  to  the  lens  and  be 
reduced  in  size;  move  the  object  closer,  and  the  image  will  form  far- 
ther away  and  be  increased  in  size. 


CHAPTER  11. 
Measurement  of  Lenses  and  Prescription  Writing, 

A  +  lens  which  brings  parallel  rays  to  a  focus  at  one  metre 
(39,37  inches)  beyond  it,  is  taken  as  the  standard  of  measure  and  is 
numbered  one.  All  others  bear  the  same  relation  to  it  that  pieces  of 
money  bear  to  $1.00. 

If  the  natural  course  of  rays  is  parallel,  and  +  1.00  changes 
their  course  so  they  meet  on  the  axis  one  metre  beyond  it,  +  2.00, 
having  twice  as  much  power,  would  cause  the  focus  to  occur  twice  as 
quickly,  or  at  one-half  the  distance  of  the  first;  +  3.00,  having  three 
times  the  strength  of  +  1-00,  would  focus  three  times  as  quickly,  or 
at  one-third  its  focal  distance;  +  .50  being  one-half  as  strong  as 
+  1.00,  would  bring  rays  to  a  focus  twice  as  far  away.  As  39.37 
inches  is  is  so  nearly  40  inches,  it  is  sulficient  for  all  practical  pur- 
poses, to  figure  on  that  basis. 

As  +  1.00  is  the  number,  and  40  inches  the  focal  length,  of  the 
unit  of  measurement,  if  we  have  the  number  of  a  lens  and  want  to 
know  its  focal  length  we  divide  the  number  into  40,  and  the  result  is 
the  figure  desired.  If  we  have  the  focal  length  and  want  the  num- 
ber, we  divide  40  by  the  focal  length  and  the  result  is  the  number, 
+  2.50  is  of  16  inches  focal  length,  because  2.50  is  contained  in  40 
sixteen  times.  A  lens  of  10  inches  focus  would  be  +  4.00  because  10 
is  contained  in  40  four  times. 


30  OPTICAL  TRUTHS. 

Lenses  are  not  made  in  smaller  fractions  than  eighths,  so  that 
when  a  figure  is  divided  into  40  and  the  result  is  not  in  eighths  we 
put  it  in  the  class  to  which  it  is  nearest.  For  example  a  15  inch 
focus  would  give  number  2.66  -3  when  the  calculation  is  made  thus: 
40  divided  by  15  equals  2.66-^.  As  2.625  is  the  nearest,  we  so  class 
it.  It  is  customary  to  ignore  the  third  figure  in  the  decimal  expres- 
sion, so  the  number  would  be  2.62  or  2.63. 

In  practice  it  is  rarely  ever  necessary  to  use  smaller  fractions 
than  quarters,  because,  if  the  eye  is  below  normal,  so  that  +  lenses 
are  required,  it  should  be  given  full  correction,  or  a  little  more;  and 
if  it  is  above  normal,  so  that  —  lenses  are  used,  it  should  be  undercor- 
rected.  That  is,  if  +  1.12  is  called  for  by  the  test,  give  +  1.25; 
if  —  1.12  is  the  test,  give  —  1.00. 

The  word  "T)ioptre"  means  "to  see  through,"  hence  it  was 
chosen  as  the  name  for  the  unit  of  measure. 

As  has  been  shown  in  the  chapter  on  refraction,  —  lenses  are  neg- 
ative quantities,  made  by  reversing  the  order  in  which  prisms  are 
used  for  +,  therefore  the  numbering  applies  to  both.  Also  to  cyl- 
inders. 

It  is  easy  to  tell  +  from  — ,  because  if  a  +  lens  is  held  between 
the  eye  and  an  object  and  moved  back  and  forth  to  right  and  left, 
or  up  and  down,  the  object  will  appear  to  move  in  the  direction  op- 
posite to  that  in  which  the  lens  is  moved,  and  the  stronger  the  lens  the 
more  decided  the  motion.  Take  —  lenses  and  the  motion  is  it'///;  the 
movement  of  the  lens. 

Spherical  lenses  have  equal  power  in  all  meridians,  while  cylin- 
drical have  power  only  when  moved  across  the  line  corresponding  to 


LENSES  AND  PRESCRIPTION  WRITING. 


31 


the  axis.  To  find  the  axis  of  a  cyHnder,  hold  it  between  the  eye  and 
some  straight  object  and  rotate  it.  The  object  will  appear  distorted 
in  shape  except  when  either  the  axis  or  the  meridian  at  right  angles 
to  the  axis  is  on  the  line  corresponding  to  the  correct  position  of  the 
object.  Having  found  that  position,  move  the  lens  sidewise  and  up 
and  down,  the  meridian  where  there  is  no  motion  to  the  object  is  the 
axis.  Make  a  mark  on  the  edge  of  the  lens  showing  where  the  axis 
is,  then  lay  the  lens  flat  on  this  figure,  centre  over  centre,  and  read  the 
meridian  from  the  figures. 


to!rJLl_ys- 


Sphero-cylinders  will  cause  the  object  to  move  in  all  directions, 
but  in  one  meridian  there  will  be  the  greatest,  and  in  the  one  at  right 
angles  to  it,  the  least  motion.  Locate  the  two  principal  meridians  as 
described  in  the  case  of  cylinders. 

To  ascertain  the  number  of  a  lens  use  lenses  of  the  opposite 
kind  which  have  the  numbers  on  them,  to  neutralize  the  one  un- 
known. If  a  +  lens  of  unknown  power  be  neutralized  with  a  —  1.00 
sphere  we  know  it  must  be  +  1.00.  If  a  +  1.00  cylinder  axis  90  stops 
all  motion  in  a  —  cylinder  we  know  it  must  be —  1.00  axis  90.  If  we 
have  a  +  compound  (sphero-cylinder)  and  —  1.00  —  1.50  axis  45 
neutralizes  it,  we  know  it  is  +  1.00  +  1.5o  axis  45.  If  it  is  a  com- 
pound and  +  1.00  —  2.50  axis  180  neutralizes  it  we  know  it  is  — 


32  OPTICAL  TRUTHS. 

1.00  +  2.50  axis  180.  There  are  such  things  as  crossed-cylinders, 
but  people  who  understand  their  business  never  have  any  use  for 
them,  except  in  the  very  rare  instances  where  the  astigmatic  error  is  so 
great  that  a  sphero-cylinder  would  give  more  spherical  and  chromatic 
aberration.  Even  then,  the  sphero-toric  lens  (one  in  which  there  is  a 
spherical  curvature  on  one  surface,  and  both  a  spherical  and  cylindrical 
curvature  on  the  other)  is  better  in  most  cases.  It  is  a  fact,  how- 
ever, that  all  compound  lenses  are  cross-cylinders  in  effect. 

Prescription  Writing. 

One  of  the  most  important  features  in  the  optical  business  is  the 
writing  of  prescriptions  correctly,  yet  more  errors  are  committed  in 
this  respect  than  in  any  other  (except  possibly,  the  prescribing  of  — 
lenses  where  +  should  be  used.) 

The  incorrect  writing  does  not  aifect  the  result  so  far  as  the  pa- 
tient is  concerned,  but  it  frequently  involves  more  work  for  the  opti- 
cian who  grinds  the  lenses.  For  example:  a  combination  written  + 
2.00 — 2.50  ax.  180  means  a  +  spherical  lens  is  combined  with  a  — 
cylindrical  with  its  axis  at  180,  or  the  horizontal  meridian. 

In  analyzing  this  we  must  remember  that  the  180  is  not  a  lens, 
but  is  the  particular  meridian  upon  which  the  axis  of  the  cylinder  is 
placed,  and  signifies  that  the  cylinder  has  no  power  there.  Next,  we 
must  remember  that  spherical  lenses  have  power  in  all  meridians 
equally,  so  the  power  of  the  combination  on  the  horizontal  meridian 
is  furnished  entirely  by  the  spherical,  and  is,  of  course,  +  2.00. 
Next,  the  other  principal  meridian  is  always  at  right  angles  to  the 
first,  which  makes  it  the  90th  meridian;  on  this  line  both  lenses  have 


LENSES  AND  PRESCRIPTION  WRITING. 


33 


power,  and  as  one  is  +  while  the  other  is  — ,  the  real  effect  is  only 
the  difference  between  them.  The  —  being  2. 50  while  the  +  is  only 
2.00,  the  balance  is  in  favor  of  the  —  by  50,  so,  when  the  combina- 
tion is  made  into  a  lens  the  power  in  its  two  principal  meridians  will 
be  represented  thus: 


-SO 


■hloo 


Had  the  prescription  been  written  — .50  +  2.5o  ax.  90  the  effect 
would  be  the  same,  because  now  the  axis  of  the  cylinder  is  vertical, 
and  it  has  no  power  on  its  axis,  while  the  —  sphere,  having  power  in 
all  meridians  takes  full  effect  on  the  vertical,  and  on  the  opposite  me- 
ridian the  +  2.50  neutralizes  the  —  .50  and  has  +  2.00  remainder. 

Manufacturing  opticians  carry  what  they  call  blank  cylinders  in 
stock;  that  is,  a  square  piece  of  glass  with  the  cylinder  ground  on 
one  surface,  and  grind  whatever  sphere  is  desired  on  the  other  side, 
then  lay  a  pattern  on  and  cut  the  lens  so  the  axis  of  the  cyhnder  is  at 
the  proper  meridian.  In  the  prescription  as  written  first  it  would  re- 
quire the  grinding  of  +  2.00  while  as  written  last  it  would  only  re- 
quire —  .50,  a  saving  of  three-fourths  of  the  work.  If  all  practition- 
ers would  observe  these  points  it  would  facilitate  greater  speed  in  fill- 
ing their  prescriptions  and  often  result  in  lighter  weight  lenses. 


34 


OPTICAL  TRUTHS. 


The  following  law  will  enable  any  one  to  tell  ^t  a  glance   if  a 
prescription  is  written  correctly: 

A  prescription  for  a  compound  lens  is  always  correct  as  it  comes 
from  the  trial  frame,  except  when  the  signs  of  sphere  and  cylinder 
differ  and  the  cylinder  is  less  than  twice  as  strong  as  the  sphere. 
+  1 .00  +  1 .00  ax.    90 


+    .50  +  1.50  ax.    45 
+  1.00  +     .75  ax.    60 

—  1.00  —  2.00  ax.  120 

—  2.00— 1.50  ax.    75 

—  1.00—  1.00  ax.  150 
+  1.00  —  2.00  ax.  135 

—  1.00  +  2.00  ax.  165 
+  1.00—  3.00  ax.  180 

—  1.50  +  4.00  ax.  140 

+  1.00  —    .50  ax.    60 
+  1.50  —  2.00  ax.  180 

—  1.00  +    .75  ax.    90 

—  1.00  +  1.50  ax.    45 


or  any  other  axis,  would 
be  correct,  because  the 
signs  are  alike;  or,  dif- 
ing,  the  cylinder  is  at 
least  twice  as  strong  as 
the  sphere. 


or  any  other  axis,  are 
wrong,  because  the  signs 
differ,  and  the  cylinder 
is  less  than  tu'iee  as 
strong  as  the  sphere. 


The  meridian  given  as  the  location  of  the  axis  of  the  cylinder  is 
called  the  first  principal  meridian  and  the  one  opposite  to  it  is  the 
second  principal  meridian. 

Having  learned  that  a  cylinder  has  no  pozcer  on  its  axis  we  have 
the  following  law  governing  the  analysis  of  compounds. 

^    ^  ^       ^        (1st  meridian,  1st  lens. 
To  Put  on  Cross  <  ^  ,        ...      ,    ,,  , 

I  2d  meridian  both  lenses. 

Now  consider  as  the  first  principal  meridian  the  line  of  the  cross 
which  requires  the  weakest  lens. 


LENSES  AND  PRESCRIPTION  WRITING. 


35 


Correct  meridian  of  least  defect  tirst,  with  a 
,  sphere.     Allow  for  its  etfect  on  the  second 
lo  lakeott  Cross -^  meridian,  and  finish  with  a  cylinder,  axis  on 

I  the  meridian  first  corrected. 
This  is  a  hvu:  because   it  always  works.     If   a  prescription  is 
written  correctly  it  will  prove  it.     If  written  incorrectly  it   will  cor- 
rect it. 

+  2.00  +  1.00  ax.  45 
+  3.00  H-^.'-^'^ 


4-  2.00  +  1.00  ax.  45  was  correct,  because  the  meridian  of  least 
defect  was  corrected  first. 

+  2.00—  1.00  ax.  180 


.fjzoc; 


+  1.00  +  1.00  ax.  90,  is  the  correction,  and  shows  the  first  written 
incorrectly  because  the  meridian  of  greatest  defect  was  corrected  first. 


36 


OPTICAL  TRUTHS. 


This  law  sometimes  exposes  a  compound  to  have  only  the  effect 
of  a  simple  cylinder,  thus: 

+  1.50—  1.50  ax.  180 
0 


•uso 


In  this  instance,  there  being  no  defect  at  one  meridian,  a  sphere 
would  be  superfluous,  as  +  1.50  ax.  90,  a  cylinder,  does  the  work  and 
the  cost  of  the  lens  is  reduced. 

Another  important  point  in  this  connection  is  that  an  expert  in 
analysis  of  prescriptions  is  able  to  tell  at  a  glance  the  name  of  the 
error  from  which  his  patient  suffers. 

For  example:  If  the  lenses  are  +,  it  means  the  eye  is  below 
normal;  if  they  are  — ,  the  eye  is  above  normal.  In  the  first  in- 
stance it  would  mean  the  retina  was  in  front  of  the  focus  of  its:own 
dioptric  system  (the  cornea,  crystalline  lens  and  humors),  and  in  the 
second  instance  the  retina  is  behind  the  focus. 
+  1.00  +  2.00  ax.  90 

^•^^^^^10%  ^^^^^'  Condition  of  etje. 


.4-3.00 


+  3.00 


LENSES  AND  PRESCRIPTION  WRITING. 


37 


Showing  the  eye  is  too  short  all  over,  but  of  greater  defect  in 
one  principal  meridian  than  in  the  other.  The  line  C  in  the  cuts  rep- 
resents the  cornea,  and  the  line  R  the  retina. 

—  2.00—  1.00  ax.  180 

Condition  of  ei^e 
R 


Fffect  of  ^e/is 


~^2J>o 


Showing  the  eye  is  too  long  all  over,  but  of  greater  defect  in  one 
principal  meridian  than  in  the  other. 

—  1.00  +  3.00  ax.  45 

fffect  uf J  e7U  ConditiorLof  ej/e 

—  »00 


R^ 


■3,00 


Showing  the  eye  too  long  in  one  meridian  and  too  short  in  the 
other. 

The  names  for  all  of  these  conditions  are  given  in  the  chapter  on 
"Refraction  of  the  Dioptric  System  of  the  Eye." 


CHAPTER  III. 
Refraction  of  the  Dioptric  System  of  the  Eye. 

In  the  dioptric  system  of  the  eye,  both  cornea  and  lens,  the  prin- 
cipal refracting  media,  are  convex.  They  therefore  belong  to  the 
same  class  as  the  convex  lenses,  which  have  been  demonstrated  to  be 
collective.  So  the  dioptric  system  of  the  eye  is  always  collective,  if 
it  is  normal,  rays  will  be  focused  on  the  retina  in  points  equally  dis- 
tributed so  that  perfect  images  of  objects  will  be  formed.  This  con- 
dition is  called  Enuuctwpia  (normal). 


r3,  n  ^ 


In  this  case  R  i  {\\\  cut)  would  be  the  retina.  C  represents  the 
cornea. 

Its  collective  powers  may  be  too  great,  in  which  case  the  effect 
would,  of  course,  be  to  bring  the  rays  to  a  point  before  reaching  the 
retina,  and  they  would  cross,  so  that  instead  of  reaching  the  retina, 
R  2,  (in  cut)  in  points,  they  would  form  a  circle  of  diffusion  of  a  di- 
ameter equal  to  xi'.     This  condition  is  called  Myopia. 

Or,  its  collective  powers  may  not  be  great  enough,  and  the 
rays  would  not  have  reached  a  point  when  they  came  in  contact  with 


40  OPTICAL  TRUTHS. 

the  retina,  R  ?  (in  cut)  when  the  interference  with  the  vision  would 
be  just  as  great,  a  b,  as  in  the  previous  instance.  This  condition  is 
called  Hyperopia  or  Hypermetropia. 

Then,  there  may  be  conditions  where  two  meridians  of  the  same 
eye  are  of  different  curvatures.     This  is  called  Astigmatism. 

There  are  five  kinds  of  astigmatism,  viz.: 

Simple  €Myopic  Astigmatism^  where  the  curvature  in  one  merid- 
ian is  normal,  and  in  another,  at  right  angles  to  the  first,  there  is  too 
much. 

Compound  [Myopic  Astigmatism,  where  the  curvature  is  too 
great  in  both  meridians,  but  is  greater  in  one  than  in  the  other. 

Simple  Hyperopic  Astigmatism,  where  the  curvature  in  one  me- 
ridian is  normal,  and  in  the  other  is  not  great  enough. 

Compound  Hyperopic  Astigmatism,  where  the  curvature  in 
neither  meridian  is  sufficient,  but  in  one  is  more  deficient  than  in  the 
other, 

[Mixed  Astigmatism,  where  the  curvature  is  greater  than  nor- 
mal in  one  meridian,  and  less  than  normal  in  the  other. 

Occasionally  a  case  is  found  where  the  curvatures  of  two  princi- 
pal meridians  not  only  differ  from  each  other,  but  the  curvature  in 
one  or  both  meridians  is  irregular,  thus  precluding  the  possibility  of 
correction  by  known  methods.     This  is  called  Irregular  Astigmatism. 

The  following  diagram  represents  the  foci  of  the  two  principal 
meridians  in  each  of  the  several  kinds  of  astigmatism.  The  line  C 
represents  the  cornea  and  the  line  R  the  retina.  It  also  shows  the 
kind  or  combination  of  lenses  which  will  be  required  for  each. 


REFRACTION  OF  THE  EYE. 


41 


5.  Hy,Flst. 


S.My.  fist. 


i-Cyl. 


-Cy(. 


CoM.Hy.  f\&t. 


Com  My.  f[st. 


+  Sph.+-Ct,l, 


'Sfjh.  -Gyl 


Mixed  fist. 


-Sph.  +  Cut, 

+  Sph.  -  Cy  I 


Defective  conditions  are  all  classed  generally  under  the  head 
^Ametropia  (meaning  abnormal).  So  any  eye  which  is  not  Emme- 
tropic is  Ametropic. 

The  refractive  properties  of  the  dioptric  system  are  of  two  kinds, 
static  and  dynamic.  The  static  is  measured  when  the  muscles  of  ac- 
commodation are  at  rest,  and  the  eye  is  adapted  to  the  most  distant 
point  at  which  it  can  see  distinctly.  This  point  is  called  punctum 
remotum  (far  point).  The  dynamic  refraction  is  measured  when  the 
accommodative  muscles  are  exerted  to  their  fullest  capacity,  and  the 
nearest  point  at  which  it  can  see  distinctly  is  called  its  punctum 
proximum  (near  point).  The  difference  between  these  two  points  is 
called  the  range  of  accommodation.    The  amplitude  of  accommoda- 


42  OPTICAL  TRUTHS. 

tion  is  the  exercise  required  of  the  muscles  to  adjust  the  eye  to  ob- 
jects between  the  far  and  near  points. 

The  simplest  manner  in  which  to  measure  the  amplitude  of  ac- 
commodation is:  First,  see  that  the  eye  is  normal  for  distance,  when 
the  nearest  point  at  which  ordinary  print  can  be  read  distinctly,  ex- 
pressed in  dioptres,  is  the  amount  of  the  amplitude  of  accommodation. 
Example:  If  a  patient  is  able  to  read  clearly  within  five  inches  of  his 
face,  we  divide  40,  the  focal  length  of  one  dioptre,  by  5,  the  focal 
length  of  the  eye,  and  the  result  is  8;  that  patient,  therefore,  has  an 
amplitude  of  accommodation  equal  to  eight  dioptres. 

Persons  with  normal  eyes  possess  the  greatest  range  of  accom- 
modation at  the  age  of  about  ten  years,  when  they  can  so  increase 
the  convexity  of  the  crystalline  lens  that  rays  from  an  object  less 
than  three  inches  from  the  cornea  will  be  focused  on  the  retina.  But 
this  power  gradually  decreases,  until,  at  the  age  of  forty,  or  there- 
about, the  loss  of  accommodation  is  so  great  that  the  near  point  is 
more  than  thirteen  inches  distant,  and  it  becomes  necessary  to  use 
spectacles  for  reading  and  near  work.  This  loss  of  accommodation  is 
called  Presbyopia. 

As  rays  of  light  coming  from  a  point  twenty  feet  distant  are 
practically  parallel,  that  distance  is  spoken  of  as  infinity,  and  the  far 
point  of  the  normal  eye  is  at  that  point,  while  the  nearest  point  is 
within  thirteen  inches. 

The  far  point  of  the  myopic  eye,  it  being  more  convex  than 
than  normal,  would,  therefore,  be  nearer  than  infinity,  and  its  near 
point  would  be  the  nearest  point  at  which,  by  exercising  its  accom- 
modation, images  would  be  formed  distinctly. 


REFRACTION  OF  THE  EYE. 


43 


The  far  point  of  the  hyperopic  eye,  would  be  beyond  infinity, 
because  it  is  less  convex  than  normal,  and  its  near  point,  like  the 
others,  the  nearest  point  at  which,  by  exerting  its  accommodation  to 
its  utmost  capacity,  clear  images  would  be  formed  on  the  retina. 

EMMETROPIA. 

( Measure,  within  the  Eye. ) 


Emmetropia  is  that  state  of  refraction  in  which  the  retina  is  sit- 
uated at  the  principal  focus  of  the  dioptric  system. 

From  the  definition  we  understand  that  the  healthy  emmetropic 
eye  ought  to  see  distinctly  at  a  distance.  This  is  true.  But  the  fact 
that  a  person  sees  more  distinctly  at  a  distance  without  than  with 
glasses,  does  not  prove  that  he  is  emmetropic.  The  definition  refers 
strictly  to  the  static  refraction,  and  a  hyperopic  eye  may  simulate 
Emmetropia,  or  even  Myopia,  from  a  spasm  of  the  accommodation. 

The  following  table  shows  the  average  power  of  accommoda- 
tion and  the  near  point  of  the  emmetropic  eye  at  several  periods  of 
life. 

dioptres, 


10  years, 

14. 

20      " 

10. 

30       " 

7. 

40       " 

4.5 

50       " 

2.5 

60       " 

1. 

70       " 

.25 

2  75  inches 

near  point. 

4  00     " 

"           " 

5.50     " 

"          " 

9.00     " 

U                     It 

16  00     " 

H                     11 

40  00     " 

<<             i; 

160.00     " 

U                    .1 

44  OPTICAL  TRUTHS. 

We  must  not  conclude  from  this  that  because  an  emmetropic 
eye,  at  40  years  of  age,  can  see  distinctly  at  nine  inches,  it  does  not 
need  the  aid  of  spectacles.  It  must  be  remembered  that  in  order  to 
bring  its  near  point  to  nine  inches,  its  maximum  power  of  accommo- 
dation is  required,  that  no  muscle  can  long  maintain  its  full  power, 
and  any  strain  upon  it  in  excess  of  that  which  is  reasonable,  works 
harm.     How  much,  then,  is  reasonable? 

If  rays  of  light  coming  from  infinity,  parallel,  will  be  brought  to 
a  focus  by  a  +  3.00  D  lens  thirteen  inches  beyond  it,  rays  started 
from  the  focal  point  would  be  divergent,  but,  upon  passing  the  lens 
would  become  parallel.  Therefore  a  +  3.00  lens  before  an  emme- 
tropic eye  would  enable  it  to  read  at  thirteen  inches  without  any  ef- 
fort of  accommodation,  because  the  rays  from  that  point  after  pas- 
sing the  lens  would  enter  the  eye  as  if  they  came  from  infinity. 
Without  such  lenses  the  dynamic  force  of  the  eye  would  have  to  be 
exerted  just  3  dioptres  to  equal  the  former  result.  At  ten  years  of  age, 
then,  after  calling  into  service  the  necessary  3  dioptres  for  reading,  the 
child  has  still  in  reserve  11  dioptres.  At  30  years,  the  last  period 
where  no  difficulty  is  experienced  in  reading  for  hours  without 
glasses,  the  reserve  force,  after  utilizing  the  3.00  D,  is  4.00  D,  which 
must  be  taken  as  the  minimum  reserve  necessary. 

Therefore,  when  the  emmetropic  eye,  at  forty  years,  is  required  to 
read  without  glasses,  the  3.00  D  deducted  from  its  maximum  power 
of  4.50  D,  leaves  it  only  1.50  D  in  reserve,  or  2.50  D  less  than  the 
standard,  and  it  is  overtaxed. 

An  eye  may  be  emmetropic  and  yet  vision  be  poor,  for  it  may 
may  be  diseased,  in  which  case  no  lenses  could  be  found  which  would 
materially  improve  vision. 


REFRACTION  OF  THE  EYE.  45 

HYPEROPIA 

(Beyond  Measure.) 


Hyperopia  is  that  state  of  refraction  in  which  the  retina  is  in 
front  of  the  principal  focus  of  the  dioptric  system. 

Hyperopia  is  not  always  a  deficency  of  length  of  an  eye  along  its 
antero-posterior  axis,  but  may  be  from  a  weakness  or  lack  of  density 
of  the  dioptric  apparatus  which  renders  it  incapable  of  focusing  rays 
upon  the  retina.  In  any  event  it  is  the  result  of  imperfect  develop- 
ment of  the  individual,  and,  in  high  degrees  is  recognized  by  the  flat- 
tened appearance  of  the  lace  and  the  diminutive  size  of  the  eyeballs 
and  corneal  area. 

The  inability  of  the  dioptric  system  of  the  hyperopic  eye  to  focus 
parallel  rays  upon  its  retina  necessitates  the  constant  use  of  a  portion 
of  its  dynamic  force,  the  amount  required  equaling  the  degree  of 
Hyperopia,  and  to  this  must  be  added  3.00  D  when  the  eye  is  used  for 
work  at  thirteen  inches.  For  example,  an  eye  which  is  hyperopic  2.00 
D  must  use  2.00  D  of  accommodation  in  order  to  see  distant  objects 
distinctly;  then,  when  the  object  is  brought  to  thirteen  inches,  3.00 
D  more  effort  is  necessary,  5.00  D  in  all.  As  the  normal  condition 
requires  no  effort  for  distance  and  3.00  D  for  the  near  point.it  is  clear 
that  the  hyperopic  eye  is  over-taxed  2.00  D  at  all  times.     It  is  not 


46  OPTICAL  TRUTHS. 

strange,  therefore,  that  individuals  so  atflicted  complain  of  sick  stom- 
ach, pains  in  eyes  and  head,  and  even  suffer  nervous  prostration,  and 
insanity  in  aggravated  cases. 

As  the  retina,  in  such  cases,  is  in  front  of  the  principal  focus,  the 
remedy  must  be  found  in  convex  lenses,  and  the  strongest  the  patient 
will  accept,  when  found  in  the  manner  described  elsewhere,  will  not  be 
too  strong.  The  object  in  prescribing  lenses  is  to  assist  Nature  in  the 
performance  of  her  functions,  not  to  supplant  her. 

It  will  be  found,  usually,  that  hyperopes  under  thirty-five  years  of 
age  will  need  no  additional  strength  of  lens  for  reading,  for  the  reason 
that  their  dynamic  refraction,  formerly  devoted  to  making  the  eye 
emmetropic,  is,  after  correction,  in  reserve  for  near  work. 

The  crystalline  lens  in  its  position  is  nearly  equivalent  to  a  11.00 
D  lens  placed  in  front  of  the  eye,  so  that  in  case  of  loss  of  this  por- 
tion of  the  dioptric  system,  through  cataract  or  otherwise,  an  eye 
which  had  been  emmetropic  before,  would  become  hyperopic,  and  an 
eye  which  was  myopic  before,  would  be  hyperopic  after,  unless  the 
myopia  exceeded  11.00  D.  The  loss  of  the  crystalline  lens  is  called 
Aphakia. 

This  error  of  refraction  is  the  most  difficult  to  fit,  on  account  of 
the  development  of  the  apparatus  of  accommodation,  which  some- 
times simulates  emmetropia,  or  even  myopia,  and,  unless  well  under- 
stood and  closely  watched  while  testing,  will  at  least  conceal  a  portion 
of  the  amount  of  hyperopia.  Therefore,  it  behooves  the  student  to 
apply  himself  particularly  to  the  mechanism  of  the  accommodation 
and  its  effects  in  such  cases,  and  also  to  the  principles  given  in  the 
"  Rules  for  Testing  "  in  the  next  chapter. 


REFRACTION  OF  THE  EYE.  47 

The  muscular  insufficiencies  which  are  often  found  associated 
with  hyperopia  are  explained  in  detail  in  the  chapter  entitled,  "Opera- 
tions, Medicines  and  Prisms,  Three  Great  Ophthalmological  Blun- 
ders." 

MYOPIA 

(To  Close  the  Eye.) 


Myopia  is  that  state  of  refraction  in  which  the  retina  is  behind 
the  principal  focus  of  the  dioptric  system. 

It  has  been  called  a  "disease  of  civilization,"  because  it  is  rarely 
found  among"  savages,  or  in  partly  civilized  countries.  It  may  be 
hereditary  or  acquired,  and  the  amount  may  be  increased  by  contin- 
uous use  of  the  eyes  at  short  distances.  In  some  instances  this 
increase  is  very  rapid  from  a  swelling  of  the  vitreous  humor,  causing 
the  eyeball  to  bulge  backward  along  the  antero-posterior  axis,  and  in 
such  cases  there  is  great  danger  that  the  retina  will  be  torn,  because  of 
its  delicate  nature,  and  the  visual  sense  seriously  impaired,  or  even 
entirely  destroyed.  Such  a  condition  is  called  a  posterior  staphyloma 
(meaning  bulging  backward).  This  is  illustrated  in  the  following 
cuts,  A  showing  the  projection  of  the  tough  sclerotic  coat  from  its 
normal  position  N,  to  X,  and  the  other  showing  the  mutilation  of  the 


48 


OPTICAL  TRUTHS. 


retina  at  M,  which  is  in  the  region  of  the  macula,  or  field  of  most 
acute  vision,  exposing  the  sclerotic  coat. 


This  condition,  called  ^Malignant  Progressive  Myopia,  occurs  in 
children,  and  is  one  of  the  most  difficult  to  treat,  because  its  origin  is 
uncertain.  Constitutional  treatment,  rest  and  the  correction  of  the 
refractive  errors,  may  result  in  checking  the  disease  until  the  patient 
reaches  maturity,  when  it  is  not  liable  to  grow  worse. 

In  ordinary  cases  the  retina  being  situated  behind  the  focus  of 
the  dioptric  system,  parallel  rays  are  brought  to  a  point  and  cross 
before  they  reach  it;  consequently,  in  order  to  see  clearly,  rays  must 
be  divergent  upon  coming  in  contact  with  the  cornea,  therefore  con- 
cave glasses  which  will  neutralize  the  excessive  convexity  of  the  eye 
are  the  remedy. 

A  myope  of  3.00  D.  would  read  at  thirteen  inches  without 
glasses,  and  without  any  effort  of  accommodation,  were  it  not  for  the 
convergence  of  the  two  eyes  which  is  necessary  to  maintain  binocular 
vision;  this  act  however,  requiring  a  supply  of  nerve  force  to  the 
internal  recti  which  is  furnished  by  the  third  nerve  (which  also  supplies 
the  muscles  of  accommodation)  stimulates  action  of  the  accommoda- 


REFRACTION  OF  THE  EYE.  49 

tion  and   increases  his  myopia.    This  explains  why,  under  the  old 
methods  of  fitting  such  cases,  so  many  are  over-corrected. 

The  muscle  troubles  of  myopes  are  caused  by  incoordination, 
not  from  excessive  nerve  strain,  as  in  hyperopia. 

ASTIGMATISM 

("Without  a  Point.) 


/ffO" 


This  cut  illustrates  the  impossibility  of  securing  a  single  point 
from  a  system  where  there  is  greater  power  in  one  meridian  than  in 
another.  It  will  be  observed  that  rays  from  the  90th  meridian  focus 
before  reaching  the  circle  around  R,  and,  having  crossed,  form  a 
circle  with  a  diameter  equal  to  the  length  of  the  lines  at  K,  while  rays 
from  the  l80th  meridian  come  to  a  point  at  %,  so  that  the  rays  from 
one  meridian  spoil  the  effect  of  the  other  and  the  result  is  no  percept- 
ible point  from  either. 

Astigmatism  is  that  state  of  refraction  where  the  retina  is  at  the 
principal  focus  of  the  dioptric  system  in  one  meridian  and  in  front  of 
or  behind  it  in  another.  Or,  where  the  retina  is  in  front  of  or  behind 
the  focus  in  both  meridians,  but  at  a  greater  distance  in  one  meridian 
than  in  the  other.  Or,  again,  where  the  retina  is  behind  the  focus  in 
one  meridian  and  in  front  of  it  in  another. 

There  are  two  seats  of  astigmatism,  the  commonest  being  in  the 
cornea.     The  other,  which  is  very  rare,  is  in  the  crystalline  lens. 


50  OPTICAL  TRUTHS. 

The  first  should  be  called  static  astigmatism ,  because  it  is  meas- 
ured when  the  eye  is  at  rest,  and  is  unchangeable.  The  second  should 
be  called  dynamic  astigmatism,  because  it  manifests  itself  usually  dur- 
ing accommodation,  and  sometimes  necessitates  an  altogether  diflferent 
correction  for  reading  from  that  for  distance.  It  is  due  to  unequal  con- 
traction of  the  ciliary  muscle,  or  a  weak  spot  in  the  lens  capsule,  or 
both,  which  causes  the  lens  to  assume  greater  convexity  in  one  meri- 
dian than  in  another.  Cases  are  found  where  the  crystalline  astigma- 
tism during  accommodation  completely  corrects  the  corneal  error,  and 
vision  is  perfect  with  a  spherical  lens.  The  astigmatism  of  the  crystal- 
line, however,  may  add  itself  to  that  of  the  cornea,  in  which  case  it 
might  be  static. 

Astigmatism  is  of  two  classes,  regular  and  irregular.  As  have 
been  enumerated  elsewhere,  there  are  five  kinds  of  regular  astigma- 
tism. Irregular  astigmatism  is  an  unevenness  of  curvature  in  addi- 
tion to  the  two  meridians  being  of  different  focal  lengths.  There  are 
cases  where  this  unevenness  affects  only  one  meridian,  and  such  cases 
may  be  corrected  by  prescribing  stenopaic  (slotted)  discs,  which  shut 
out  the  light  from  all  except  the  meridian  of  symmetrical  curvature. 

The  astigmatic  eye  does  not  receive  upon  its  retina  a  perfect 
image  of  objects  at  any  distance.  The  accommodative  apparatus 
attempts  to  afford  a  remedy,  but  of  course  fails,  because  its  power  is 
exerted  equally  in  both  meridians,  and  the  difference  between  them 
remains  the  same;  the  only  result  being  strain  upon  the  nervous  and 
muscular  systems,  headaches,  nausea  and  general  discomfort  to  the 
individual. 

The  remedy  is  a  lens  or  combination  of  lenses  which  will  equal- 
ize the  curvatures. 


REFRACTION  OF  THE  EYE.  51 

ANISOMETROPIA. 

(Unequal  Vision.) 

Anisometropia  is  that  condition  in  which  the  refraction  of  the 
two  eyes  is  decidedly  different,  causing  vision  to  be  unequal. 

It  is  not  uncommon  to  find  a  tritling  difference  between  the  eyes, 
but  they  are  not  classified  as  anisometropia  until  the  difference  is  suf- 
ficient to  cause  discomfort,  or  possible  loss  of  acuteness  in  one. 

There  are  three  kinds  of  anisometropia,  (1),  where  both  eyes  fix 
at  once,  and  binocular  vision  exists;  (2),  where  each  eye  is  used 
alternately;  (3),  where  one  eye  only  is  used,  the  other  being  perma- 
nently excluded. 

This  defect  has  been  the  cause  of  much  argument  with  reference 
to  its  correction.  Oculists  who  base  their  conclusions  on  their  knowl- 
edge of  materia-medica  exclusively,  for  the  reason  that  they  have 
never  educated  themselves  to  consider  the  mechanics  of  the  anatomy, 
argue  that  there  is  a  "  point  of  toleration,"  in  the  acceptance  of  cor- 
rection, similar  to  the  "  point  of  toleration  "  of  drugs. 

This  is  not  true.  The  correction  should  be  made  as  early  as 
possible,  and  the  practitioner  should  inform  himself,  and  his  patient, 
of  the  reason  for  the  disturbance,  which  is  that,  whereas,  an  abnormal 
relation  did  exist,  to  which  the  nervous  system  was  compelled  ta 
adapt  itself,  and  that  relation  being  disturbed,  required  a  readaptation 
to  the  new  condition,  it  would,  for  a  time,  affect  the  entire  system, 
causing  great  discomfort;  but,  being  a  mechanical  change,  it  is  only 
a  matter  of  a  few  days,  or  weeks,  until  the  new  order  is  established, 
and  all  is  satisfactory. 

If  the  vision  in  one  eye  is  very  poor,  and  the  other  is  good,  and 
the  correcting  glasses  do  not  bring  the  bad  eye  up  to  the  standard  of 


52  OPTICAL  TRUTHS. 

the  good  one,  it  is  good  practice  to  reduce  vision  in  the  good  eye  to 
the  standard  of  the  bad  one,  by  over-correcting  with  +  or  under- 
correcting  with  —  lenses.  After  a  few  weeks,  if  the  bad  one  shows 
no  signs  of  improvement,  it  is  because  the  nerve  is  affected,  and 
the  attempt  to  equahze  them  will  have  to  be  abandoned.  Some- 
times the  correction  of  the  bad  eye  brings  it  up  just  enough  to  inter- 
fere with  the  comfort  of  the  good  one,  and  it  may  be  left  off  entirely, 
not  because  the  patient  would  not  "  tolerate  "  it  after  a  time,  but 
because  it  does  no  good,  and  only  causes  an  unnecessary  drain  upon 
the  nervous  system.  Common  sense  should  always  be  used  in  such 
.matters. 

PRESBYOPIA. 

(Old  Sight.) 

While  Presbyopia  is  not  an  error  of  refraction,  it  is  entitled  to  a 
place  in  this  chapter,  because  the  dynamic  refraction  is  changed  by  it, 
so  that  glasses  are  required  for  reading  purposes  even  by  Emme- 
tropes.  It  is  the  only  one  of  all  refractive  troubles  which  is  caused  by 
advancing  years,  and  comparatively  young  people  bring  it  on  by 
over- working  the  nerves  which  supply  the  muscles  of  accommodation. 

It  is  a  loss  of  nerve  force,  and  of  the  elasticity  of  the  crystalline 
lens  and  its  associates  in  the  mechanism  of  accommodation. 

The  usual  working  point  is  1 3  to  16  inches  from  the  eyes;  there- 
fore, after  an  eye  is  made  emmetropic,  whether  with  +  or  —  lenses, 
if  it  cannot  adjust  itself  to  near  points,  it  will  require  +  spherical 
lenses  over  the  others. 

As  the  emmetropic  eye  is  already  adapted  to  rays  coming  par- 
allel to  its  axis,  it  follows  that  it  will  never   need  a  stronger  lens  than 


REFRACTION  OF  THE  EYE.  53 

the  number  represented  by  the  distance  the  object  is  from  the  eye.  To 
read  at  16  inches  will  never  require  more  than  +  2.50,  because  that  is 
enough  to  start  the  rays  into  the  eye  parallel  to  the  axis.  To  read 
at  l3  inches  will  never  require  more  than  +  3.00.  At  10  inches,  + 
4.00,  etc. 

As  l3  inches  is  the  usual  reading  distance,  3.00  D  is  the  total 
amount  of  presbyopia  one  can  have,  although  many  eminent  writers 
have  compiled  wonderful  tables  to  show  that  it  may  be  8.00  D,  or 
even  more.  This  is  not  so,  for  the  reasons  shown  in  the  paragraph 
above.  Any  power  over  +  3.00  used  for  reading  at  l3  inches  repre- 
sents hyperopia.  They  also  assume  to  fix  the  amount  of  lens  required 
at  different  ages,  which  is  impossible. 

In  adding  for  reading  to  a  correction  for  an  error  of  refraction, 
the  addition  is  spherical  only,  and,  of  course,  the  cylinder  (if  there 
be  one)  is  not  changed.     Thus,  a  prescription  for  distance  being: 

L.  +  1.00  +  '.75  ax.  90 

R.  +  1.00  +  1.00  ax.  60 

add  +  2.00  for  reading,  would  be 

L.  +  3.00  +  .75  ax.  90 

R.  +  3.00  +  1.00  ax.  60 
If  the  prescription  for  distance  read: 

L.  —  3.00  —  2.00  ax.  180 

R.  —  2.50—  1.50  ax.  180 

add  +  3.00  for  reading,  it  would  be 

L.  —  2.00  ax.  180 

R.  +  .50— 1.50  ax.  180 
In  this  case  the  reading  lens  for  the  left  eye  would  be  a  simple 
cylinder,  and  for  the  right,  a  compound,  mixing  +  and  —  . 


54  OPTICAL  TRUTHS. 

Sometimes  the  addition  for  reading  results  in  the  prescription  for 
the  reading  glass  being  written  incorrectly  according  to  the  law  of 
prescription  writing.     Thus: 

L.  +  1.00—  2.50  ax.  180 

R.  +  2.00  —  4.00  ax.  45 

add  +  2.00  for  reading,  would  be 

L.  +  3.00  — 2. 50  ax.  180 

R.  +  4.00  —  4.00  ax.  45 
which  is  technically  incorrect,  but,  putting  it  on  the  cross  and  analy- 
zing it,  we  write  it  correctly,  thus: 

L.  +  .50  +  2.50  ax.  90 

R.  +  4.00  ax.  135 
Remember,  after  the  correction  for  distance  is  made,  the  addition 
for  reading  is  given  to  both  eyes  at  once,  and  the  added  lenses  must 
be  of  equal  power. 

The  amount  added  for  reading  depends  upon  whether  accommo- 
dation is  totally  or  only  partially  gone.  The  object  of  the  lenses  is 
to  do  as  much  of  the  work  as  the  patient  is  unable  to  perform.  I 
have  never  found  occasion  to  use  less  than  +  1.00  in  such  cases,  and, 
of  course,  never  more  than  +  3.00  for  l3  inches. 


CHAPTER  IV. 
The  'Toggingf''  Method  of  Measuring  Errors  of  Refraction. 

Of  all  appliances  and  methods  for  measuring  errors  of  refraction 
those  which  involve  the  least  complication  and  give  the  best  results 
should  commend  themselves  most  highly  to  the  practitioner. 

The  Fogging  system  of  using  the  trial  lenses  is  the  only  one  which 
aifords  at  once  simplicity,  speed,  accuracy,  opportunity  to  test  bin- 
ocular vision,  accommodation,  the  muscles  and  reduces  the  necessity 
for  the  use  of  mydriaties  to  emergency  cases. 

It  should  be  remembered  "fogging"  involves  a  principle,  and, 
to  make  it  a  success,  the  broad  scope  of  that  principle  must  be  under- 
stood thoroughly. 

Roles  for  Proceed  ure. 

First — Question  the  patient.  This  means  the  general  health, 
special  ills  of  the  past  and  present,  such  as  headaches,  indigestion, 
constipation,  piles,  loss  of  appetite,  female  disorders,  hysteria,  nerv- 
ous debility,  etc.,  all  are  factors  which  assist  in  the  diagnosis  of  cases. 

Second — Examine  the  retina  with  the  ophthalmoscope,  by  the 
direct  method,  which  affords  a  view  of  the  real  article,  not  a  picture 
of  it,  as  is  seen  by  the  indirect  method. 

Third — Adjust  the  trial  frame  so  the  pupils  are  perfectly  cen- 
tered therein,  cover  each  eye,  alternately,  with  the  black  disc,  and  di- 


56  OPTICAL  TRUTHS. 

rect  the  patient  to  read  aloud  the  letters  on  the  trial  card,  which  should 
be  at  a  distance  of  fifteen  or  twenty  feet.  The  lines  on  the  card  are 
all  numbered  and  the  figures  over  each  line  indicate  the  distance  in 
feet  (or  metres)  at  which  that  line  is  read  by  the  normal  eye.  There- 
fore if  a  patient  is  seated  fifteen  feet  from  the  card  and  the  smallest 
line  which  can  be  read  correctly  with  ease  is  the  one  numbered  thirty, 
the  acuteness  of  vision  with  that  eye  is  expressed  thus,  ^f .  If  patient 
is  twenty  feet  away,  and  reads  the  same  line,  it  would  be  expressed 
f  |[.  If  the  metric  system  is  used  on  the  card  the  twenty  feet  line  will 
be  numbered  6  and  the  thirty  feet  line  9,  so  the  acuteness  would  be 
expressed  |.  By  either  system  such  a  result  would  indicate  only 
two-thirds  of  the  normal  acuteness  is  present. 

Fourth — If  there  be  a  dilTerence  in  the  acuteness  of  the  two, 
correct  the  best  one  first,  because,  it,  having  been  accustomed  to  doing 
the  most  work,  will  accept  the  proceeding  more  intelligently,  and 
thus,  by  way  of  the  brain,  aid  in  securing  the  best  results  on  its  fellow. 
Permit  no  one  in  the  operating  room  but  yourself  and  the  patient. 
Begin  the  test  by  placing  in  ihefrontcell  of  frame  a  -4-  sphere  of  suf- 
ficient strength  to  fog  or  blur  vision  so  patient  cannot  see  better  than 
number  200,  or  the  largest  type  on  the  card.  Direct  that  constant 
attention  be  paid  to  keeping  the  eyes  fixed  toward  the  card,  because 
if  they  are  turned  upon  nearer  objects  it  stimulates  action  of  the  ac- 
commodation and  interferes  with  the  work.  Now  begin  with  —  .25 
and  — .50  spheres,  holding  one  in  each  hand.  Stand  at  patient's  right, 
with  the  left  hand  resting  lightly  on  the  forehead,  the  right,  with 
handle  of  lens  between  the  thumb  and  first  finger,  while  the  second 
and  third  fingers  touch  the  cheek  just  enough  to  enable  you  to  hold 


FOGGING  SYSTEM  OF  TESTING.  57 

the  lens  steady.  Try  the  weaker  one  first,  than  the  stronger.  Of 
course  the  last  one  will  be  best,  then  replace  the  — .25  in  the  case,  re- 
taining the  —  .50  and  take  a  —  .75.  Compare  them  as  before,  mak- 
ing the  change  from  one  to  the  other  quickly  after  patient  has  shown 
what  line  can  be  read,  then  if  the  — .75  is  best,  put  the  —  .50  in  the 
case  and  get  —  1.00  for  comparison  with  the  —  .75.  When  a  de- 
cided improvement  is  shown  by  patient  reading  three  or  four  lines  it 
is  good  practice  to  take  two  lenses  of  the  same  power,  say  two  — .  75s 
and  compare  them  in  the  manner  described,  as  the  improvement 
shown  by  the  second  lens  at  each  comparison  has  taught  patient  to 
expect  it,  and  the  elTect  of  this  is  to  aid  in  coaxing  the  nerve  supply 
of  the  accommodation  to  cease  acting.  In  other  words  the  patient  is 
deceived  by  the  trick,  which  should  be  repeated  as  often  as  benefit  is 
shown,  only  increasing  the  strength  of  the  —  lens  .25  at  a  time  as 
needed  until  vision  is  almost  as  good  as  it  was  with  the  naked  eye.  If 
+  3.00  is  the  fogging  lens,  and  by  our  test  we  find  —  1.75  held  in 
front  of  it  permits  §]}  dimly  when  vision  was  f f  plainly  with  the 
naked  eye,  it  is  time  to  stop.  Now  the  differences  between  +  3.00 
and  —  1.75  is  +  1.25  which  is  the  spherical  part  of  the  correction. 
Therefore,  put  +  1.25  in  the  rear  cell  of  frame  before  removing  the 
fogging  lens. 

Fifth— Search  for  astigmatism  by  directing  attention  to  astig- 
matic charts  comprising  various  designs,  figures  or  letters,  formed  by 
lines  arranged  at  different  angles  in  the  several  figures.  If  all  appear 
equally  distinct  the  astigmatism  is,  at  most,  very  slight.  If  some  of 
the  figures  appear  plain  while  others  appear  blurred  it  proves  astigma- 
tism, and  the  two  principal  meridians  of  the  eye  are:  one  correspond- 


58  OPTICAL  TRUTHS. 

ing  to  the  black  lines  and  the  other  at  exactly  right-angles  to  it.  The 
meridian  at  right- angles  to  the  black  lines  is  the  one  which  \s  corrected, 
and  the  one  corresponding  to  the  black  lines  is  the  uncorrected  one. 
This  seems  paradoxical  to  the  beginner,  and  I  have  heard  "  ocuHsts" 
say  they  knew  it  to  be  a  fact  but  could  not  tell  why.  Anyone  can 
solve  the  problem  quickly  by  noting  that  the  action  of  a  +  cylinder 
on  light  is  to  converge  it  to  aline  corresponding  to  the  axis.  It  is  the 
curvature  in  the  opposite  meridian  which  does  this,  and  the  same  is 
true  of  any  irregular  dioptric  system,  including  the  eye.  To  correct 
the  astigmatism  take  —  cylinders,  —  .25  and  —  .50,  as  in  the  former 
proceeding  with  spheres,  and  hold  them  in  front  of  the  eye,  axis  at 
right-angles  to  the  black  lines,  until  one  is  found  which  makes  all  the 
figures  of  the  chart  appear  equally  distinct  the  instant  the  lens  is  in 
position,  taking  care  to  use  the  weakest  cylinder  which  has  the  desired 
elYect. 

Another  method  of  measuring  the  astigmatism  is:  After  getting 
the  spherical  part  of  the  correction,  place  the  stenopaic  (slotted)  disk 
in  the  front  cell,  with  the  slot  horizontal,  have  patient  read  the  lettered 
chart  as  before,  then  turn  the  slot  to  various  positions  and  if  vision  is 
better  at  one  place  than  at  others  it  proves  astigmatism.  After  noting 
the  acuteness  of  vision  in  the  best  meridian  turn  the  slot  to  the  posi- 
tion at  right  angles  to  it,  and  proceed  with  —  spheres,  holding  them 
in  front  as  before,  until  one  is  found  which  makes  vision  almost  as 
good  as  it  was  with  the  slot  in  the  first  position.  The  weakest  lens 
which  will  do  this,  gives  the  power  of  cylinder  required.  Laying  the 
sphere  aside,  take  a  —  cylinder  of  corresponding  strength  and  put  it 
in  place  of  the  slot,  with  its  axis  on  the  meridian  where  the  slot  first 
stood,  this  gives  the  power  in  the  desired  meridian. 


FOGGING  SYSTEM  OF  TESTING.  59 

Sixth — Test  the  other  eye,  in  the  same  manner. 

Seventh— Leaving  the  correction  before  both  eyes,  cover  each 
alternately,  that  patient  may  compare  vision,  and,  if  there  is  any  dif- 
ference, correct  it. 

Eighth — Test  the  power  of  accommodation,  by  having  patient 
see  how  close  to  his  face  he  can  read  a  line  of  ordinary  newspaper 
print.  If  this  near  point  is  less  than  six  inches,  and  the  patient  has 
never  worn  glasses  constantly,  those  prescribed  for  distance,  accord- 
ing to  the  prescription  written  from  the  contents  of  the  frame,  will  be 
sufficient  for  all  purposes. 

Ninth— If  the  near  point  is  farther  away  than  six  inches,  or,  if 
the  patient  has  been  wearing  glasses  constantly,  and  complains  that 
the  eyes  tire  when  reading,  have  the  paper  held  at  the  greatest  distance 
the  individual  expects  to  hold  near  work,  and  apply  +  spheres,  (the 
same  strength  for  each  eye),  to  both  eyes  at  once,  in  front  of  the 
distance  correction  already  in  the  frame.  Begin  with  +  3.00  and 
change  them  for  weaker  ones  until  a  pair  is  found  which  permits  com- 
fortable vision.  These  will  be  the  "addition  for  reading,"  and  if 
patient  desires  bifocals,  so  state  in  your  prescription.  If  two  pairs 
are  wanted,  say  so.  The  optican  who  fills  your  prescription  will  do 
the  rest. 

Tenth — Test  the  muscles.  The  simplest  method  is  to  place  be- 
fore one  eye  a  double  prism,  and  before  the  other  a  plane  red  glass, 
covering  it  with  the  dark  disk.  Direct  attention  to  a  light  placed 
about  twenty  feet  distant,  and  rotate  the  double  prism  until  two  white 
lights  are  seen,  one  directly  above  the  other.  Then  uncover  the  other 
eye,  and  if  the  muscles  are  normal  (orthophoria)  the  red  light  will 


60  OPTICAL  TRUTHS. 

appear  in  line  with  and  half  way  between  them.  If  they  are  out  of 
position  it  is  Heterophoria  (abnormal),  if  the  deviation  is  to  right 
and  left  from  the  center,  it  is  Exophoria  if  the  lights  separate,  and 
Esophoria  if  they  cross  over.  The  eyes  in  muscular  insufficiencies 
always  deviate  the  same  way  the  lights  do.  if  the  deviation  is 
up  or  down  and  out,  it  is  Hyperexophoria,  and  if  up  or  down 
and  in,  it  is  Hyperesophoria.  To  measure  the  amount  of  trouble, 
prisms  must  be  held  in  front  of  one  eye  (it  makes  no  difference 
which)  until  one  is  found  which  brings  all  three  lights  in  normal  po- 
sition. If  the  base  of  the  prism  is  toward  the  nose  it  proves  the 
internal  recti  are  too  active.  If  the  base  is  the  other  way,  the  internal 
recti  are  too  weak.  The  cause  of  the  first  is  excessive  strain  upon  the 
nerves  which  supply  the  muscles  of  accommodation  and  the  internal 
recti;  the  result  is  a  contraction  of  the  latter  and  the  eyes  are  pulled 
out  of  equilibrium.  The  cause  of  the  second  is  a  weakness  of  the 
same  nerve  from  the  strain  upon  it,  and  this  conclusion  is  further 
established  by  an  accompanying  weakness  of  the  accommodative 
power.  If  the  base  of  prism  is  up  or  down  it  signifies  weakness  of 
the  superior  rectus  in  one  eye  or  the  inferior  in  the  other.  If  it  is  in 
an  angular  position,  it  shows  several  muscles  are  involved.  The 
weak  muscles  are  always  under  the  apex  of  the  prism.  Prisms  to  be 
worn  constantly  should  never  be  prescribed  for  these  troubles.  Correct 
the  errors  of  refraction  and  prescribe  rest  for  a  week  or  so,  and  Nature 
will  cure  the  muscle  trouble. 

Deviations  from  the  Roles. 

There  are  some  extraordinary  cases,  in  the  treatment  of  which  it 
will  be  found  necessary  to  deviate  from  these  rules,  because  of  inter- 


FOGGING  SYSTEM  OF  TESTING.  61 

mittent  nerve  force,  which  enables  the  patient  to  see  well  through  the 
slot  one  moment  and  fail  to  see  anything  clearly  an  instant  later;  or, 
the  patients  idiosyncrasies  may  interfere  with  the  strict  application  of 
any  rules;  or,  the  error  of  refraction  may  be  so  great,  and  of  such  a 
character,  (as  a  high  degree  of  astigmatism),  that  only  the  general 
principles  implied  by  the  rules  can  be  utilized.  Hence  the  necessity 
for  a  clear  comprehension  of  the  principles. 

If,  after  fogging  a  patient  whose  vision  is  very  poor,  say  j^^^, 
with  the  naked  eye,  the  fogging  lens  must  be  entirely  neutralized 
before  vision  returns  to  j%%,  it  proves  +  spheres  will  not  be  of 
benefit,  so  it  is  proper  to  remove  the  fogging  lens  and  try  the  slot 
alone  in  the  several  meridians  according  to  rule  tive,  and  if  one  meri- 
dian is  worse  than  the  other  it  will,  of  course,  be  corrected  with  a  +  or 
—  cyUnder.  Then  if  vision  is  still  below  flj  it  may  be  improved 
with  —  spheres  held  in  front  of  the  cylinder. 

Again,  vision  may  be  very  poor  and  no  sphere  will  be  accepted, 
nor  can  the  slot  be  used  successfully.  Then  try  cylinders,  beginning 
with  quite  a  strong  +,  say  +  3.00,  rotate  it  slowly  before  the  eye  and 
if  it  improves  vision  at  one  point  and  makes  it  worse  at  another,  it 
proves  astigmatism.  Place  the  axis  at  the  point  where  it  gives  best 
vision  and  proceed  to  increase  or  decrease  its  power,  if  vision  is  im- 
proved thereby,  until  the  best  results  are  obtained. 

It  should  be  remembered  it  is  not  always  possible  to  improve 
vision  to  |^,  and  sometimes  it  is  not  possible  to  improve  it  at  all. 
But  when  this  is  the  case  it  is  something  more  than  an  error  of  refrac- 
tion. 

Another  case   may  have  poor  vision,  /o^V,  and  no  spheres  or 


62  OPTICAL  TRUTHS. 

cylinders  will  be  of  service,  but  when  the  slot  is  placed  in  one  posi- 
tion there  is  marked  improvement,  'l^.  When  the  slot  is  turned 
to  the  other  meridian  vision  is  dim  and  nothing  will  improve  it.  In 
such  cases  it  is  proper  to  prescribe  the  slot,  which  can  be  made  of 
brass  or  vulcanized  rubber.  The  necessity  for  this  peculiar  device  for 
aiding  vision  is  irregular  astigmatism,  in  which  one  meridian  has  a 
symmetrical  curvature  while  the  other  has  not,  and  consequently  can- 
not be  corrected.  In  this  instance  the  good  meridian  was  emmetropic, 
but  it  might  have  been  hyperopic  or  myopic,  and  the  correcting  lens 
combined  with  a  slot,  in  which  case  the  proper  lens  would  have  to  be 
frosted  or  shellaced,  except  at  the  opening,  which  is  usually  about  one 
millimetre  wide  and  ten  to  twenty  millimetres  long.  It  is  possible  for 
two  principal  meridians  to  be  of  regular  curvature  and  all  others  un- 
even, requiring  a  cross-slot,  and  this  might  be  combined  with  correct- 
ing glasses  for  those  two  meridians. 

If  spheres,  and  cylinders,  and  slots  all  fail,  sometimes  the  pin- 
hole disc,  which  shuts  out  all  but  the  axial  rays,  alTords  such  im- 
provement that  the  patient  is  very  happy  to  wear  it  constantly.  Of 
course  the  hole  would  be  made  as  large  as  possible  and  good  vision 
maintained. 

Caution. 

If  a  patient  comes  complaining  of  headache  or  other  symptoms 
of  hyperopia,  and,  by  the  test  seems  to  be  a  myope  of  less  than  1.00 
D,  do  not  prescribe  —  lenses  without  first  atropizing  the  patient,  be- 
cause it  is  very  likely  that  the  case  is  one  of  hyperopia  with  a  ionic 
spasm  of  accommodation,  which  is  a  permanent  involuntary  cramp 
of  the  sphincter  muscles  of  the  ciliary  processes. 


FOGGING  SYSTEM  OF  TESTING.  63 

If  —  lenses  are  required  to  fit  a  patient,  always  use  the  weakest 
which  will  give  the  results  desired.  A  good  rule,  in  this  connection, 
is  to  give  the  weakest  lenses  which  will  give  |{}  vision  and  then  steal 
from  the  spherical  part  of  the  correction  .25  or  .50  D  to  reduce  vision 
to  ^^ 

As  long  as  a  patient  can  see  as  well  through  a  +  lens  as  without 
it,  it  is  not  too  strong. 

As  long  as  a  patient  sees  as  well  without  —  lenses  as  with  them, 
never  prescribe  them. 

if  —  .50  ax.  90  gives  ||}  vision,  prescribe  +  .50  ax. '90  if  it 
gives  f  {}  vision,  even  if  the  first  was  found  under  a  mydriatic.  And 
if  —  200  ax.  180,  or  any  other  strong  —  cylinder  gives  f^,  and  the 
patient  still  has  accommodation,  prescribe  +  .25  or  +  .50  sphere  in 
connection  with  the  cylinder  and  reduce  vision  to  f  {}.  It  saves  a  little 
nerve  strain  when  coming  up  to  the  reading  point,  but  the  chief  idea 
in  this  precaution  is  to  avoid  overcorrecting  myopia. 

If,  in  testing,  vision  is  quite  good  one  moment  and  the  next  is 
not  so  good  by  several  lines  on  the  test  card,  it  indicates  clonic  spasm 
of  accommodation  (an  involuntary  and  intermittent  action),  and  to 
overcome  it,  the  patient  must  be  secluded  from  the  presence  of  others 
who,  by  talking  might  interfere  with  the  control  of  his  nervous  sys- 
tem. But,  if  vision  is  good  when  the  patient  begins  to  read  a  line,  and 
it  gradually  fades  away  before  him,  it  is  the  optic  nerve  which  is  af- 
fected, and  absolute  rest  must  be  ordered,  to  be  continued  several 
days.  Or,  by  atropizing,  the  3d  nerve  supply  may  be  shut  off  en- 
tirely, leaving  a  greater  force  for  the  2d  or  optic  nerves. 


64  OPTICAL  TRUTHS. 

Qinical  Hints. 

If  a  patient,  with  the  naked  eye,  sees  some  of  the  lines  of  the 
astigmatic  charts  more  plainly  than  others,  it  proves  astigmatism,  but 
it  does  not  prove  what  kind.  Ordinarily  if  the  vertical  lines  are 
plainest  it  indicates  myopic  astigmatism,  and  if  the  horizontal  lines 
are  plainest  it  indicates  hyperopic  astigmatism,  but  it  is  by  no  means 
certain  that  such  is  the  case.  Only  the  test  will  tell.  The  best  meri- 
dian of  the  eye  is  always  at  right  angles  to  the  plain  lines. 

After  correcting  a  high  degree  of  myopia  in  children,  it  will, 
often,  be  found  necessary  to  add  +  for  reading,  but  the  constant 
wearing  of  the  correction  will  develope  the  accommodation  so  that 
after  a  few  weeks  or  months  the  +  will  be  no  longer  needed. 

The  wearing  of  glasses  for  hyperopia  has,  often,  wonderful  cos- 
metic effects.  Ladies,  whose  faces  have  become  rough  and  wrinkled 
prematurely  from  the  constant  elTort  to  overcome  the  hyperopia,  will 
find  both  defects  have  disappeared  in  a  short  time.  The  reason  for 
this  is  that  the  contraction  of  the  nervous  system  prevented  the  free 
circulation  of  nerve  force,  the  blood  supply  was  diminished,  and  the 
function  of  the  lymphatics  was  practically  cut  otT.  After  correction 
all  these  are  restored  and  the  complexion  improves. 

The  contraction  of  the  sphincter  muscles  throughout  the  body, 
in  the  etTort  to  overcome  hyperopia  by  accommodation,  causes  men- 
strual difficulties  in  females,  and  piles  in  both  males  and  females. 
Hence  it  follows  that  the  correcting  glasses  will  remove  the  cause  and 
Nature  will  restore  normal  conditions,  unless  the  trouble  has  existed 
too  long. 

Epilepsy  is  a  nervous  disease,  and  very  often  finds  its  origin  in 


FOGGING  SYSTEM  OF  TESTING.  65 

hyperopia,  the  full  correction  of  which  sometimes  acts  with  almost 
miraculous  promptness. 

If  a  patient  is  in  a  debilitated  condition  and  needs  different  glasses 
for  distance  and  near  work,  insist  upon  two  pairs,  instead  of  bifocals. 
Or  "  grab  fronts  "  may  be  used  for  reading. 

The  correcting  glasses  in  hyperopia  often  improve  the  hearing  of 
persons  partially  deaf,  by  permitting  additional  nerve  supply  to  be 
sent  to  the  auditory  nerves. 

Correcting  glasses  often  make  patients  sick  at  the  stomach,  be- 
cause the  entire  nervous  system  has  to  adapt  itself  to  the  new  condi- 
tions. Energy  which  has  been  demanded  for  the  eyes  is  now  left  in 
the  chief  nerve  center,  and  it,  being  unaccustomed  to  such  a  liberal 
supply,  goes  into  hysterics,  if  you  please,  and,  like  a  child  with  a  new 
toy,  requires  several  days  to  restore  its  equilibrium;  in  the  meantime 
it  sends  nerve  force  in  every  direction  to  see  if  some  function  is  in 
need  of  it.  It  sometimes  surprises  the  stomach  so  that  vomiting  oc- 
curs. Do  not  be  frightened  by  the  old  "  spook  "  that  such  incidents 
mean  the  patient  will  not  "tolerate"  the  correction.  Explain  the 
situation  and  tell  patient  to  stick  to  it,  and  all  will  be  well. 

Sometimes,  in  a  high  degree  of  hyperopia,  the  accommodation  will 
be  so  completely  exhausted  that,  when  corrected,  the  patient  will  not 
be  able  to  read.  In  persons  under  thirty  years,  or  thereabout,  the  ac- 
commodation will  be  all  right  in  a  few  weeks. 

If  a  patient  reads  |f  with  the  naked  eye  it  only  proves  he  is  not 
a  myope  and  that  he  has  no  disease  which  affects  the  eye. 

If  he  cannot  read  |{f,  he  may  be  a  hyperope,  or  a  myope,  or 
an  emmetrope  with  diseased  eyes. 


66  OPTICAL  TRUTHS. 

If  he  reads  better  than  |^  it  proves  he  is  a  hyperope,  and  it  is 
not  uncommon  to  find  as  much  as  1.00  or  1.50  D. 

Tmted  glass  should  not  be  used  for  lenses  intended  for  constant 
wear.  In  cases  of  Photophobia,  (an  aversion  to  light),  the  cause  is  an 
error  of  refraction  or  a  disease  which  has  alTected  the  retina,  making 
it  hypersensitive  and  the  tinted  glass  only  aggravates  the  trouble. 
Correct  the  error  and  give  constitutional  treatment. 

Colored  glasses  without  focus  should  not  be  prescribed  save  for 
exceptional  cases,  such  as  excursions  on  snow  or  water,  or  when  the 
eyes  are  diseased  so  that  it  is  imperative  some  protection  be  afforded. 
Then  prescribe  plane  smoke.  Never  use  the  coquills,  they  have  — 
cylindrical  effects. 

Anyone  with  an  error  of  refraction  should  wear  glasses  con- 
stantly; the  hyperope  to  relieve  nerve  strain,  and,  incidentally,  to  im- 
prove vision  if  it  is  below  normal;  the  myope  to  improve  vision  and 
permit  coordinate  action  of  the  muscles  of  accommodation  and  con- 
vergence. 

After  the  eye  has  matured,  which  is  at  about  the  age  of  eight  or 
ten  years,  if  the  correction  is  equal  to  the  error  no  change  of  lenses 
will  ever  be  needed.  When  presbyopia  comes,  at  forty  or  thereabout, 
additional  spherical  power  will  be  needed  for  near  work  only.  This 
will  be  increased  from  time  to  time,  as  accommodation  fails,  until  + 
3.00  is  reached,  which  will  be  all  that  will  be  needed,  unless  the  in- 
dividual desires  to  work  on  objects  nearer  than  thirteen  inches. 


CHAPTER  V. 
Machine  Tests — Objective  and  Subjective  Methods  Compared. 

Under  this  heading  come  Ophthalmoscopy,  Retinoscopy,  Op. 
thalmometry,  Refractometry,  Prismometry,  etc. 

Objective  tests  are  those  in  which  the  patient  takes  no  part,  in 
the  sense  of  using  his  visual  powers,  the  correction  being  assumed  to 
be  determined  by  refraction  and  reflection  of  light  from  the  observed 
eye. 

Subjective  tests  are  those  in  which  the  patient's  attention  is 
directed  to  some  object,  while  lenses  or  other  devices  are  applied,  and 
judgment  is  formed  by  what  he  sees. 

Each  method  has  its  advocates  and  all  are  more  or  less  enthus- 
iastic according  as  their  knowledge  of  optics  is  developed.  They  all 
belong  to  the  science,  and  each  has  its  points  of  excellence,  under  the 
manipulation  of  the  expert.  Here  they  shall  be  considered  from  the 
standpoint  of  their  availability  to  the  average  practitioner. 

The  Ophthalmoscope,  as  a  means  of  measuring  errors  of  refrac- 
tion, is  only  an  approximate  in  the  hands  of  the  most  accomplished 
expert,  because,  (l),  it  has  nothing  less  than  .50  D.  lenses;  (2),  it  is 
necessary  that  the  observer's  errors  be  corrected;  (3),  the  observer 
must  control  his  accommodation  absolutely;  (4),  the  patient  must  be 


68 


OPTICAL  TRUTHS. 


under  the  intluence  of  a  mydriatic.  A  very  common  paragraph  in  op- 
tical books  is  one  in  which  the  operator  tells  how  he  "  corroborated  " 
his  other  tests  with  this  instrument.  I  have  never  yet  seen  one  which 
stated  the  ophthalmoscope  test  had  been  corroborated  by  the  subject- 
ive test.     Let  us  be  honest. 


The  Retinoscope,  on  account  of  its  cheapness,  and  its  halo  of 
mystery  to  the  patient,  has  its  enthusiastic  patrons,  who  claim  it  is 
the  only  test,  that  all  other  appliances  were  made  in  vain.  It  is,  un- 
doubtedly, a  very  interesting  method,  simple  and  reasonably  accurate 
in  the  hands  of  any  one  who  will  give  time  to  practice. 

The  enthusiastic  retinoscopist,  who,  in  a  recent  number  of  an 
optical  journal,  asserted  that  if  a  patient,  under  the  subjective  test, 
could  not  determine  whether  he  could  see  better  with  +  .25  ax.  90  or 
—  .25  ax.  180,  and  the  operator  would  prescribe  the  first  when  the 


MACHINE  METHODS  OF  TESTING.  69 

second  was  needed,  it  would  double  the  astigmatism,  only  demonstra- 
ted that  he  has  not  even  a  rudimentary  knowledge  of  optics. 

The  operator  sits  40  inches  (one  metre)  from  the  patient,  with  a 
plane  or  concave  mirror,  and  reflects  the  light  from  a  lamp  placed 
over  or  to  one  side  of  the  patient,  care  being  taken  that  his  face  is 
well  shaded  from  all  but  the  reflected  light.  Patient  directs  his  visual 
axis  a  little  to  one  side  of  operator,  who  will  then  see  a  red  reflex 
from  the  pupil,  and  by  rotating  the  mirror  on  its  vertical  axis  the  re- 
flected field  will  move  back  and  forth  horizontally  across  the  pupillary 
space,  when  a  shadow  will  interfere  with  the  circular  illumination  of 
the  pupil.  If  the  plane  mirror  is  used  the  shadow  will  go  -with  the 
operator's  motion  in  hyperopia  and  emmetropia,  and  against  it  in 
myopia.  If  the  concave  mirror  is  employed  the  effect  is  reversed,  the 
motion  will  be  against  in  hyperopia  and  emmetropia,  and  with  in 
myopia.  The  trial  frame  is  put  on  patient's  face,  and  +  or  —  lens 
placed  therein  until  one  is  found  which  stops  all  shadows  or  else 
reverses  the  motion  slightly. 

Having  found  the  lens  which  stops  the  shadow  in  one  meridian, 
record  it,  and  proceed  with  the  opposite  meridian  in  the  same  manner. 
If,  after  correction,  it  is  found  the  two  meridians  required  different 
strengths  of  lens  to  fix  them,  say  +  3.00  on  the  horizontal  and  + 
2.00  on  the  vertical,  astigmatism  is  present,  and  the  prescription  would 
be  +  2.00  +  1.00  ax.  90.  As  the  operator  was  seated  only  one 
metre  distant,  the  patient  is  corrected  to  that  point,  and  is,  therefore, 
a  myope  of  1.00  D.  To  remedy  this  the  spherical  part  of  the  correc- 
tion must  be  reduced  1.00  D,  making  the  correct  prescription  +  t.OO 
+  1.00  ax.  90.  Should  —  lenses  be  required  the  same  condition  would 
be  present  at  the  close  of  the  test,  but  to  correct  it  1.00  D  must  be 


70  OPTICAL  TRUTHS. 

added  to  the  spherical  part  of  the  correction.  If  it  is  a  case  of  mixed 
astigmatism,  where  +  and  —  lenses  are  combined,  the  same  condi- 
tion would  exist.  If  the  spherical  part  is  —  it  must  be  increased  1.00 
D,  and  if  it  is  +  it  must  be  decreased  1.00  D.  If  the  shadows 
move  obliquely  when  the  mirror  is  rotated  on  the  vertical  or  horizontal 
meridians,  it  indicates  oblique  astigmatism  and  the  rotation  of  the 
mirror  will  be  changed  to  the  corresponding  meridians. 

If  +  or  —  spheres  stop  the  shadow  in  all  meridians  it  is  simple 
hyperopia  or  myopia.  Of  course,  if  the  +  sphere  is  1.00  D  only, 
it  indicates  emmetropia,  and  if  it  is  less  than  +  1.00  it  indicates  a 
low  degree  of  myopia. 

Obstacles  which  interfere  with  its  more  general  adoption  are:  (1), 
the  practice  required  to  become  sufficiently  expert  to  render  it  even 
approximately  reliable;  (2),  the  objection  of  patients  to  having  the 
light  thrown  into  the  eye;  (3),  the  necessity  for  the  dilatation  of  the 
pupil  and  suspension  of  accommodation  by  the  use  of  mydriatics. 


The  Ophthalmometer  is  claimed  by  its  friends  to  be  the  only 
means  of  obtaining  exactly  the  axis  of  corneal  astigmatism,  and  they 


MACHINE  METHODS  OF  TESTING.  71 

say  it  will  measure  the  amount  approximately.  It  is  not  adapted  to 
the  measure  of  hyperopia  or  myopia.  It  is  an  impressive  instrument 
as  will  be  seen  from  the  cut,  and  from  that  standpoint  may  be  worthy 
of  a  place  in  the  testing  room. 


Among  the  subjective  tests  the  Refractometer  shown  above  is 
entitled  to  a  very  high  position  among  instruments.  It  imbodies  the 
"fogging"  principle  in  a  very  large  measure,  and  is  certainly  the 
greatest  aiixiUiaiy  to  the  trial  set  yet  oiTered  to  the  public.  It  pre- 
sents a  fine  appearance,  and  is  of  practical  utility  in  the  correction  of 
all  errors  of  refraction,  speedily  and  accurately.  The  reasons  it  is  not 
a  substitute  for  the  trial  set  are:  (1),  it  is  a  monocular  instrument,  and 
vision  of  the  two  eyes  cannot  be  compared  after  correction  without 


72  OPTICAL  TRUTHS. 

exciting  the  accommodation;  (2),  it  cannot  be  used  to  test  for  read- 
ing distance;  (3),  it  cannot  be  used  for  testing  the  muscles.  However, 
none  of  these  qualities  are  claimed  for  it,  so  they  cannot  be  put  forth 
as  objections. 


The  Prisoptometer  is  another  subjective  test  which  is  adapted  to 
the  "  fogging  "  system.  Its  essential  principle,  as  its  name  indicates, 
is  prisms,  A  double-prism  is  set  in  the  eye-piece,  which  is  attached 
to  the  pointer  (C  in  the  cut).  The  patient's  attention  is  directed  to- 
ward a  target  placed  at  a  definite  distance,  and  when  the  pointer  is 
placed  in  a  vertical  position,  he  will  see  two  targets,  one  above  the 
other.  As  the  pointer  is  rotated  it  rotates  the  prisms,  and  the  targets, 
which  are  circular,  will  move  around  each  other.  If  they  touch,  it 
indicates  emmetropia,  or  hyperopia  with  active  accommodation;  if 
they  lap,  it  indicates  myopia;  if  they  separate,  it  indicates  hyperopia; 
if  they  lap  or  separate  more  at  one  place  than  another,  it  is  as- 
tigmatism. The  fogging  is  done  by  placing  +  lenses  in  cells  at- 
tached in  front  of  the  eye  piece.    The  same  points  of  difference  which 


MACHINE  METHODS  OF  TESTING.  73 

make  the  Refractometer  only  auxilliary  to  the  trial  set,  apply  to  this 
instrument. 

There  are  optometers,  astigmometers  and  other  minor  instru- 
ments without  number,  all  of  which  have  their  "talking  points," 
and  involve  optical  principles  to  some  extent.  They  cannot  hope  for 
a  permanent  place  in  the  practitioner's  rooms. 


CHAPTER  VI. 
The  Clinical  Value  of  Perfectly  Adjusted  Frames  and  Lenses. 

It  is  just  as  necessary  that  spectacles  or  eye-glasses  fit  the  face, 
as  it  is  for  the  lenses  to  neutralize  the  defects  of  refraction;  for,  if  the 
frame  does  not  fit,  or  the  lenses  chance  to  be  decentered,  the  practi- 
tioner's work  will  be  a  failure. 

The  trial  frame  is  of  little  use  in  taking  the  measurements,  except 
that  it  gives  the  pupillary  distance.  The  important  points  are  the 
three  measurements  of  the  nose,  vi^:  its  height  above  the  pupillary 
line,  its  width  inside  at  the  widest  point,  and  the  inclination  of  the 
crest,  whether  back  of,  forward,  or  on  a  plane  with  the  lenses. 

Have  three  frames  of  the  following  dimensions: 

(1)  Nose  high,  W  inch;  wide,  H  inch;  crest  on  plane  of  lenses. 

(2)  Nose  high,  >s  inch;  wide,  H  inch;  crest  back  of  plane  of 
lenses  }i  inch. 

(3)  Nose  high,  j\  inch;  wide,  %  inch;  crest  back  of  plane  of 
lenses  yi  inch. 

With  these  anyone  can  fit  any  nose,  by  making  allowances  which 
will  be  suggested  at  once  when  the  frame  is  on  the  face. 

The  sizes  of  lenses  run  from  small  to  large:  Nos.  3,  2,  1,  0,  00, 
Jumbo,  and  there  can  be  no  fixed  rule  regarding  what  size  to  prescribe 
except  that  in  rimless  goods  a  size  larger  should  be  used  than  would 


76  OPTICAL  TRUTHS. 

be  put  in  frames.  The  size  and  shape  of  the  face  have  much  to  do 
with  the  size  of  glasses,  and  the  best  way  to  be  sure  about  this  is  to 
have  a  few  samples  for  exhibition  and  trial  purposes.  A  narrow- 
faced  child  would  require  a  2-eye  size  to  get  the  proper  proportion  be- 
tween the  pupil  and  temple  distances,  while  a  large  round-faced  man 
would  require  the  largest  size  to  look  well  and  secure  a  width  of 
temples  which  would  cause  them  to  clear  the  sides  of  his  face. 

An  old  frame  to  which  the  customer  attaches  value  on  account 
of  its  associations,  and  which  does  not  fit,  can  be  made  to  do  so  by 
putting  in  a  new  nose-piece. 

Eye-glass  frames  are  adjustable,  and  in  all  ordinary  cases  where 
there  is  sufficient  nose  to  afford  a  resting  place  for  the  guards  no 
measurements  need  be  sent  to  the  optician.  In  ordering  the  new- 
fangled guards,  secure  directions  from  their  makers. 

To  duplicate  frames,  measure  the  pupil  distance,  temple  distance, 
nose  height,  width,  and  inclination  of  crest,  five  measurements  in  all, 
upon  cards  made  for  the  purpose,  which  any  optical  house  will  fur- 
nish free  of  charge. 


PART  IL 


CHAPTER  I. 
Exposing  Ophthalmological  Charlatans  and  Their  Practices. 

"  There  are  tricks  in  all  trades — except  ours." 

This  is  an  expression  which  has  been  used  for  ages  by  the  sly  ones 
of  all  trades  and  professions,  to  inform  their  acquaintance  and  the 
public 'of  the  fact  that  there  are  opportunities  for  dishonest  practice  in 
every  occupation.  It  is  the  seed  from  which  has  sprung  the  general 
distrust  in  the  minds  of  the  laity,  and  its  reaction  has  involved  many 
bright  scholars,  who  are  honest  in  every  other  particular,  in  dishonest 
treatment  of  their  patrons,  and  they  have  trained  their  consciences  to 
acquiesce  in  the  rascality  by  the  explanation  that  if  they  did  not  hum- 
bug their  victims,  some  one  else  would. 

In  what  is  stated  here  regarding  the  charlatans  of  the  ophthalmic 
profession  let  it  be  understood  distinctly  there  is  naught  of  malice,  nor 
fear  of  the  censure  which  it  may,  possibly,  inspire. 

There  are  two  classes  of  charlatans  in  ophthalmic  practice:  (l), 
those  who  are  ignorant  of  the  fundamental  laws  of  refraction,  and  of 
the  relation  between  the  eyes  and  the  rest  of  the  anatomy  through  the 
nervous  system;  (2),  those  who  know  their  business  but  use  question- 
able methods  for  mercenary  reasons. 

Each  of  these  classes  is  divided  into  two  branches  which  are  often 
found  arrayed  against  each  other:  (a),  the  medical  doctors;  {b),  the 
refractionists.  The  result  of  their  contentions  is,  the  public  becomes 
suspicious  of  both. 


80  OPTICAL  TRUTHS. 

It  is  the  author's  behef  that  instead  of  erecting  barriers  of  laws 
to  shut  out  from  practice  any  class,  those  barriers  should  be  built  from 
the  more  enduring  material  of  general  education  upon  the  subject, 
which  will  enable  the  patron  to  choose  between  the  true  and  the  spuri- 
ous practitioner,  and  it  is  his  hope  that  the  contents  of  this  book  may 
not  only  aid  in  the  education  of  the  masses,  but  that  it  may  show 
clearly  the  spheres  of  classes  "a"  and  "b,"  referred  to  above,  and 
reconcile  each  to  the  existence  of  the  other. 

Much  of  the  ignorance  comprised  in  class  "  1  "  is  the  elTect  of  an 
affection  we  will  call  "  hero-worship,"  which  afflicts  many  otherwise 
good  people,  who  believe  every  assertion  they  find  in  the  books  of 
eminent  authors,  simply  because  of  their  eminence.  And  it  is  only 
fair  to  their  eminences  to  say  that  in  some  cases  they  have  been  mis- 
understood, or  they  have  been  misquoted  by  instructors  and  others 
who  have  read  or  heard  of  their  works. 

One  of  my  students,  a  young  physician,  came  into  the  class-room 

recently  and  announced  he  had  just  heard  that  Dr. claimed  to 

have  cured  a  case  of  consumption  by  the  use  of  prisms,  and  added 
that  he  would  be  d — d  before  he  would  believe  it. 

I  replied,  "  me  to,",  but  at  once  explained  that  Dr. never 

made  any  such  pretentions,  1  had  read  his  own  statement  regarding  the 
case  which  was  evidently  meant,  and  in  it  he  said  he  visited  an  old 
friend  who  was  bed-fast  with  consumption,  that  he  operated  on  her 
recti  muscles,  and,  two  years  later,  learned  the  woman  had  recovered; 
and,  as  her  improvement  dated  from  his  operation,  he  naturally  con- 
cluded he  had  at  least  contributed  in  no  small  degree  to  the  cure. 

The  gentleman  who  gave  the  young  doctor  such  information  was 
one  of  those  "  fool  friends  "  who  do  one  more  harm  than  good.     He 


EXPOSING   OPHTHALMOLOGICAL  CHARLATANS.  81 

had;  evidently,  never  read  Dr. 's  book;  but,  knowing  prisms  were 

his  hobby,  he  jumped  at  the  conclusion  that  victory  perched  on  the 
prism  banner. 

The  principal  charlatan  is  the  self-styled  "oculist,"  who,  under 
cover  of  a  medical  license  and  an  admantine  cheek,  without  preparing 
himself  especially  for  the  work,  opens  for  business  in  swell  apartments 
and  proceeds  to  humbug  the  people  in  a  manner  which  ought  to  make 
the  shade  of  P.  T.  Barnum  moan  with  envy.  First,  he  consults  the 
patient,  sometimes  free  of  charge;  second,  he  proceeds  to  examine  the 
eyes  with  the  ophthalmoscope  by  the  "  indirect  method,"  by  which  at 
best  he  could  only  see  an  inverted  picture,  (the  majority  of  them 
never  see  anything  but  the  anterior  portion  of  the  globe,  the  cornea  and 
iris,  because  they  direct  the  patient  to  roll  his  eyes  like  a  sick  cow, 
while  they  look  wise  and  horrified);  third,  he  atropizes  the  eyes  and 
proceeds  to  convince  the  patient  that  prompt  and  vigorous  medical 
treatment  is  needed,  which  will  require  bi-weekly  visits  to  the  oculist, 
at  $2  per  visit,  just  as  long  as  the  victim  will  stand  it.  After  a  while 
he  prescribes  glasses,  the  measures  for  which  are  taken  in  a  haphaz- 
zard  manner,  without  even  the  semblance  of  a  system. 

An  Example:  A  young  man  of  26  was  attending  a  dental  col- 
lege and  his  eyes  began  to  trouble  him  (pain  and  conjunctivitis).  He 
went  to  one  of  these  "  oculists."  He  was  ordered  to  quit  college  and 
report  for  treatment  at  least  once  in  two  weeks,  which  he  did  for 
about  eight  months,  being  treated  each  time  to  a  touch  of  silver  nitrate 
or  some  other  equally  noxious  chemical.  On  the  occasion  of  the 
third  or  fourth  visit  he  was  given  a  pair  of  glasses  as  follows: 
L.  +  .75  +  .50  ax.  90 
R.  +  1.50 


82  OPTICAL  TRUTHS. 

Finally,  when  the  "  oculist  "  informed  him  an  operation  would 
be  necessary,  his  patience  became  exhausted,  he  refused  to  be  tritled 
with  any  further,  and  his  brother  brought  him  to  me.  I  found  a 
simple  hyperopia  of  2.50  D. 

When  informed  he  was  not  in  a  serious  condition  he  was 
skeptical,  and  when  I  told  him  a  little  cool  salt  water  would  cure  his 
conjunctivitis  in  a  week,  now  that  he  would  have  his  correction,  he 
laughed  incredulously.  It  required  only  four  days  for  him  to  get 
well,  nevertheless. 

This  brings  us  to  the  first  point  of  gross  ignorance,  or  crimin- 
ality, whichever  word  suits  the  person  who  practices  it.  Not  one 
such  case  as  the  above  described  in  a  hundred  needs  medical  treat- 
ment, and  it  is  a  crime  against  Nature  to  use  escharotics  on  the  con- 
junctiva, or  corneal  cells.  The  cause  of  most  cases  of  conjunctivitis 
is  hyperopia,  in  which  the  strain  upon  the  ciliary  muscles  sets  up  an 
inflammation  which  is  communicated  to  the  conjunctiva  and  lids, 
then  the  patient  suddenly  exposes  his  eyes  to  the  cold  winds  and  the 
sphinctre  nerves  and  muscles  at  the  mouths  of  the  Meibomian  glands 
contract,  preventing  the  performance  of  their  functions,  and  the  mat- 
ter is  forced  backward  between  the  conjunctiva  and  lids  which  be- 
come "  granulated."  Medicines  will  not  cure  that  condition.  They 
may  relieve  it  temporarily,  but,  the  cause  still  existing,  the  trouble 
will  recur.  Correct  the  hyperopia,  use  an  antiseptic  lotion  for  a  few 
days  and  Nature  will  do  the  curing. 

Another  Example:  A  young  lady  of  22,  was  brought  in  by 
a  student  who  could  not  muster  courage  enough  to  attempt  the  case 
after  she  told  him  she  had  been  operated  upon   twice,  and  had  four- 


EXPOSING    OPHTHALMOLOGICAL  CHARLATANS.  83 

teen  pairs  of  glasses,  powers  varying  from  .50  to  1.25  D,  from  half 
a  dozen  oculists  of  this  city.  Examination  revealed  the  fact  that  the 
first  operation  was  tenotomy  of  the  internal  recti,  and  the  second  was 
advancement  of  the  internal  recti.  1  found  her  hyperopic  2.00 
D,  gave  her  full  correction,  and  a  month  later  she  told  the  student  it 
was  a  pleasure  to  live,  although  at  first  she  wanted  to  throw  the 
glasses  away  on  account  of  the  blurred  vision,  etc. 

Another  Example:  Young  lady,  aged  20,  was  "  treated"  for 
six  months  by  one  of  the  best  known  "  oculists  "  in  this  country, 
who  finally  gave  her 

L  +  2.00—  5.00  ax.  180 

R  +  2.00—  5.00  ax.  180 

With  these  glasses  she  could  see  f  {[  with  the  left  eye  and  /o*V  with 
the  right.  Without  them  vision  was,  L  |{|^,  R  y-/o-  There  was  no 
diseased  condition  when  1  saw  her,  nor  had  there  been.  I  made  a 
test  and  found  the  following: 

L  —  .75  +  2.25  ax.  90 

R  —  5.00  ax.  180 

These  gave  f  {}  vision  in  each  eye.  She  had  worn  his  prescrip- 
tion faithfully  for  several  months,  because  her  father  said  the  doctor's 
instructions  must  be  followed.  She  says  she  never  had  either  com- 
fort or  vision  until  she  got  the  last  pair. 

Now,  some  one  will  question  her  ability  to  see  equally  well  with 
her  left  eye,  naked,  or  with  his  lens  on,  so  let  us  analyze  the  eye  from 
my  prescription  which  must  be  right,  because  she  has  both  comfort 
and  good  vision. 


84 


OPTICAL  TRUTHS. 


-.lir 


■t-lfO 


■HfO 


The  diagram  at  the  left  shows  the  power  of  the  lens  combina- 
tion  on  its  two  principal  meridians,  while  the  one  at  the  right  shows 
the  foci  of  the  two  principal  meridians  of  the  eye  with  reference  to- 
the  retina,  which  is  represented  by  the  line  "  R." 

Now,  put  on  +  2.00  —  5.00  ax.  180  and  the  ertect  on  the  prin- 
cipal meridians  of  the  eye  will  be: 


-t-nr 


It  will  be  seen  that  in  either  instance  one  meridian   is  within 

.75  of  the  retina  which  accounts  for  her  having  as  good  vision  with. 

as  without  the  lens. 

Not  so  with  the  other  eye: 

R 


EXPOSING   OPHTHALMOLOGICAL  CHARLATANS. 


85 


With  his  correction  on  the  condition  would  be  thus: 


showing  why  vision  in  this  eye  was  worse  with  than  without  the 

lens. 

There  is  a  pubhcation  which  advertises  itself  as  the  greatest  of  its 
kind  and  says  "  its  editors  and  contributors  are  the  cream  of  the  pro- 
fession.'"    Let  us  examine  specimens  of  their  work: 

On  page  5  of  its  January,  1897  issue  the  Ophthalmic  Record  has 
a  contribution  under  the  heading  "Metamorphopsia"  in  which  seven 
cases,  measured  under  atropine,  are  recorded,  and  the  lenses  which 
were  prescribed  are  given. 

Case  hi  L  H  +  3.50  ax.  90  H 

R  _2^Q_  _  1^00  +  5.00  ax.  1.20  f^ 

This  cut  shows  the  condition  of  the  eyes  as  deduced  from  the 
lenses. 

+  3.i"0 


3.ro 


+  W.00 


86 


OPTICAL  TRUTHS. 


Here  is  what  the  contributor  prescribed: 
L  +  1.25  ax.  90 
R  —  1.00  +  3.50  ax.  120 

And  here  is  the  condition  of  the  eyes  with  the  lenses  on: 


-hiJff 


It  is  evident  the  glasses  prescribed  did  not  even  approximate  a 
correction  of  the  error. 

Case  iv.  L  f  a  +  i5o—  3.00  ax.  \.SS  %^ 
RU  +  1-00  —  1-00  ax.  180  ft 


Zeft 


/?/^U. 


-f  '.5-'^ 


-/,r» 


-»-  i>"" 


-i-roo 


-h/fiO 


EXPOSING    OPHTHALMOLOGICAL  CHARLATANS 

He  prescribed 


87 


L  —  3.00  ax.  155 

R  _  1.00  ax.  180    with  this  effect: 


Xeft 


Tf/yixt. 


Here  he  has  left  uncorrected  1.50  D  hyperopia  in  one  eye  and 
1 .00  D  in  the  other. 

Case  v.  L  %%  +  3.50  ax.  90  \% 
^\%  +  3.50  ax.  90|{[ 

He  prescribed  +  3.00  ax.  90  for  each  eye,  leaving  .50  D.  as- 
tigmatism uncorrected  in  each  eye. 

In  three  of  the  remaining  cases  he  prescribed  the  full  correction  in 
myopia  and  none  of  the  patients  were  over  27  years  of  age.  This  in- 
volves the  maximum  strain  upon  the  accommodation  when  reading, 
a  thing  which  common  sense  ought  to  forbid. 

If  such  are  the  "  cream  of  the  profession  "  for  humanity's  sake 
let  us  take  the  skimmed  milk. 

Several  years  ago  a  lady  was  fitted  by  one  of  these  "  oculists  " 
after  atropinization  for  two  weeks:  L  —  1.00  —  2.00  ax.  180; 
R  _  1,00  —  3.00  ax.  ISO.  She  never  had  good  vision.  I  recently 
gave  her  L  -  1.00  -f  6.50  ax.  180;  R  -  2.00  +  6.50  ax.  180,  and 
she  had  f^  vision  at  once.  Her  eyes  have  not  changed;  they  were 
not  fitted  before. 


88 


OPTICAL  TRUTHS. 


I  saw  a  "  prescription  "  from  one  of  the  "  experts  "  at  the  Illi- 
nois Eye  and  Ear  Infirmary,  recently.  It  was  written  on  the  back  of 
one  of  the  cards  of  admission  to  the  poor.     Here  it  is  verbatim. 


<C^  = 


K 


r-v. 


1  -X^ 


It  was  sent  to  me  by  an  optician  for  interpretation.     I  presumed 
the  patient  was  the  victim  of  a  retinoscope  fiend  and  that  the  lines 
meant  the  meridians  of  the  eye  so  I  made  the  following  from  it: 
R.  +  4.00  +  .50  ax.  90 
L.  +  2.00  +  .50  ax.  90 
But  I  suggested  that  as  vision  was  so  much  worse  with  the  left 
than  with  the  right  to  begin  with,  it  was  very  evident  the  prescription 
was  not  even'an  approximate  to  the  error. 


EXPOSING    OPHTHALMOLOGICAL  CHARLATANS.  89 

If  this  is  the  kind  of  work  they  do  free  at  such  institutions  it  is 
time  there  were  some  laws  passed  to  protect  the  pubHc. 

Another  charlatan  is  the  man  who  does  his  "  fitting  "  with  the 
ophthalmoscope,  retinoscope  ophthalmometer,  etc. ,  or,  at  least,  he 
"  corroborates  "  his  trial  set  test  with  these  instruments.  In  view  of 
the  fact  that  the  ophthalmometer  only  measures  corneal  curvatures 
and  its  manufacturers  only  claim  it  is  accurate  as  to  the  meridian 
where  the  axis  of  cylinder  should  be  placed,  and,  as  the  ophthalmo- 
scopes in  general  use  have  no  lenses  less  than  .50  D,  the  transparency 
of  their  proposition  exposes  it  at  a  glance. 

The  utility  of  the  retinoscope  is  doubtful,  but  it  is  infinitely 
superior  to  either  of  the  others.  The  instruments  all  have  their  place, 
but,  excepting  the  ophthalmoscope,  all  of  them  could  be  consigned  to 
the  scrap-pile  and  no  one's  eyes  would  suffer  in  consequence. 

The  ophthalmoscope  is  invaluable  in  studying  the  internal  por- 
tion of  the  eye,  but  as  an  instrument  to  measure  errors  of  refraction 
accurately,  no  one  but  a  fakir  would  claim  it. 

It  is  the  class  herein  described  who  constantly  cry  for  "  protec- 
tion "  by  law  from  "non-professionals."  Whenever  these  cries  are 
heard,  look  out  for  incompetents.  The  ophthalmologist,  or  physi- 
cian, or  other  professional  person  who  knows  his  business,  and  prac- 
tices it  honestly,  needs  nothing  but  acquaintance  to  establish  himself 
more  securely  than  it  would  be  possible  for  any  law  to  do. 


CHAPTER  11. 

Operations^  Medicines  and  Prisms,  Three  Great  Blunders. 

It  is  unfortunate  for  his  patients  when  a  physician  arrives  at  the 
conclusion  he  is  greater  than  Nature,  and  the  situation  becomes  truly 
alarming  when  we  find  the  several  text  books  and  schools  of  medicine 
innoculating  their  students  with  such  an  idea,  which  has  established  a 
reputation  second  to  none  for  virulence. 

No  physician  ever  cured  anyone  with  medicines,  operations,  or 
by  any  other  means.  Skillful  doctors  have  sometimes  rendered  such 
assistance  to  Nature  that  she  was  able  to  effect  cures,  but  in  many  in- 
stances she  was  compelled  to  combat  both  the  disease  and  the  med- 
icines prescribed  by  the  incompetent  physician. 

The  three  great  blunders  in  ophthalmic  practice  are  operations, 
medicines,  and  the  indiscriminate  use  of  prisms.  The  reason  for  their 
existence  is  that  blind  faith  in  preceptors,  referred  to  in  another  chap- 
ter, together  with  a  lack  of  ambition  in  each  individual  to  acquire  ad- 
ditional knowledge  by  his  own  researches. 

The  function  of  an  engine  is  to  be  the  medium  through  which 
motive  power  is  applied;  and,  without  the  force  to  operate  it,  it  is 
useless.  It  is  the  same  with  the  muscles — cut  oft"  their  nerve  supply 
and  they  cease  to  act. 

It  is  obvious  the  practitioner  should  understand  the  mechanism 
of  the  organ  with  which  he  has  to  deal,  and,  without  this  knowledge 
he  is  a  dangerous  person. 


92  OPTICAL  TRUTHS. 

The  dioptric  apparatus  of  the  eye  is  controlled  directly  by  the 
3d  nerve,  which  supplies  the  sphincter  muscles  of  both  the  ciliary  pro- 
cesses and  the  iris;  and,  in  order  that  the  direction  of  the  visual  axis 
may  harmonize  with  the  focus  of  the  system,  four  of  the  rotary 
muscles  are  placed  in  charge  of  the  same  nerve,  viz:  the  internal 
superior,  inferior  recti  and  inferior  oblique.  The  amount  of  nerve 
supply  required  by  the  ciliary  muscles  in  the  act  of  accommodation 
regulates  the  supply  to  the  internal  rectus  especially.  Thus  if  the 
normal  eye  is  accommodating  to  a  point  one  metre  distant,  the  con- 
vergence required  to  maintain  binocular  vision  involves  a  strain  of 
one  dioptre  on  the  branches  of  the  3d  nerves  which  supply  the  in- 
ternal recti.  It  may  be  computed,  therefore,  that  for  each  dioptre  of 
accommodation  required  in  each  eye  there  is  an  additional  strain  of 
one-half  of  that  amount  for  convergence. 

For  Example:  The  average  amount  of  work,  required  from  the 
eyes  of  persons  engaged  in  near  work,  is  three  hours  per  day. 
The  usual  working  distance  is  about  thirteen  inches.  In.  emmetropia 
this  would  require  3  D  accommodation  for  each  eye,  and  3  D  of 
convergence  from  bolh,  making  a  total  of  9  D.  Now,  let  us  figure  by 
the  second,  60  x  9  =i  540  D  per  minute;  and  540  x  60  =  32.400 
D  per  hour;  and  32.400  x  3  =  97.200  D,  or  the  total  amount  of 
nerve  force  used  each  day  in  the  normal  condition. 

The  sensibility  of  the  optic  nerve  has  been  termed,  very  properly, 
the  "  guiding  sensation,"  because,  so  long  as  the  power  of  vision  re- 
mains, it  is  practically  in  control  of  all  our  movements.  The  motions 
of  the  eyeballs,  therefore,  are  subject  to  orders  from  the  macula,  via. 
the  optic  nerve,  to  the  brain,  thence  through  the  3d,  4th  or  6th  nerves 
to  the  point  where  power  is  needed. 


THREE  GREAT  BLUNDERS.  93 

Another  Example:  A  hyperope  of  2  D,  in  order  to  focus  light 
from  infinity  upon  the  retina,  must  accommodate  2  D,  and  the  nor- 
mal tendency  to  converge  to  the  20-inch  point,  with  that  much  ac- 
commodation would  cause  diplopia  but  for  the  demands  of  the 
"  guiding  sensation,"  which  calls  for  sut^lcient  power  to  be  sent  to  the 
external  recti  through  the  6th  nerves  to  prevent  that  convergence. 
This  requires,  at  least,  2  D  of  nerve  force,  thus  we  have  2  D  accom- 
modation in  each  eye,  2  D  convergence  and  at  least  2  D  to  restrain 
that  convergence,  making  a  total  of  8  D  per  second.  So,  figuring 
as  in  the  other  example,  we  have  8  x  60  =  480  D  per  minute;  480 
X  60  =  28,800  per  hour;  and,  as  the  hyperope  uses  his  accommoda- 
tion all  the  time,  for  16  hours  daily,  we  have  28,800  x  16  =  460,- 
800  D  per  day.  Then,  if  he  has  the  same  work  to  do  as  the  emme- 
trope,  we  add  the  97,200  D  to  the  460,800,  making  a  total  strain 
upon  the  nervous  system  of  the  hyperope,  558,000  D  daily.  Com- 
pare this  with  the  normal  97,200  D.  The  extra  460,800  must  come 
from  the  reserve  supply  of  nervous  energy  stored  in  the  brain,  and, 
when  that  is  exhausted,  trouble  begins. 

These  troubles  include  conjunctivitis,  muscular  insufficiencies, 
and  all  sorts  of  nervous  affections,  from  simple  headache,  to  insanity, 
including  periodical  sick-headaches,  dyspepsia,  piles,  nervous  prostra- 
tion and  female  diseases. 

If  the  foregoing  statement  is  true,  it  follows  as  a  simple  matter- 
of-course,  unless  the  derangement  of  the  system  has  existed  so  long 
that  chronic  organic  disease  has  resulted,  that  the  proper  and  only 
treatment  needed  is  a  complete  correction  of  the  hyperopia,  together 
with  such  rest  and  other  hygienic  observations  as  common  sense  will 


94  OPTICAL  TRUTHS. 

dictate  to  any  one  with  a  little  knowledge  of  the  functions  of  the 
nerve  force  and  mathematical  ability  to  solve  easy  problems. 

Even  in  chronic  diseases,  the  correction  of  the  hyperopia  will 
assist  the  patient's  recovery,  and,  in  order  that  a  full  appreciation  of 
this  proposition  may  be  had,  I  will  make  the  broad  assertion  that  so 
long  as  sufficient  vitality  remains  to  keep  the  atflicted  one  out  of  bed, 
the  treatment  suggested  will  et^'ect  a  complete  cure  in  ninety  per  cent. 
of  all  such  cases. 

Now,  for  the  proofs:  First,  attention  is  called  to  the  fact  of  the 
unnatural  nerve  strain  in  hyperopia,  as  has  been  shown,  and  these 
questions  asked:  Would  not  such  strain  have  bad  effects?  Would  not 
such  effects  be  in  proportion  to  the  amount  of  error  and  the  work  re- 
quired? 1  say,  emphatically,  yes.  Second,  I  will  cite  a  few  of 
hundreds  of  cases  which  it  has  been  my  privilege  to  treat,  with  the 
results: 

Mrs.  R.,  aged  30,  came  with  a  cross-eyed  boy,  because  she  had 
heard  1  cured  such  difficulties  without  operation,  which  is  sometimes 
possible,  but  in  this  case  the  child  was  too  young — only  four  years. 
She  inquired  the  cause  of  his  trouble,  and  I  informed  her  it  was  fre- 
quently a  heritage  from  parents  with  defective  eyes.  She  indignantly 
declared  that  neither  she,  her  husband,  nor  any  member  of  either 
of  their  families  had  ever  needed  glasses,  and  expressed  her  opinion 
of  my  statement  in  most  unflattering  terms. 

As  she  prepared  to  leave,  she  said  to  the  child,  "  Come  on,  dear; 
let  us  go  home.  Mamma  has  such  a  headache  she  can  scarcely  sit 
still."  1  asked  if  she  often  suffered  from  such  attacks,  and  she  re- 
plied: "  Almost  constantly,  and  at  least  once  in  two  weeks  I  have  to 


THREE  GREAT  BLUNDERS.  95 

remain  in  bed  for  a  day  or  so."  Further  questioning  elicited  thie  state- 
ments that  she  had  "  swallowed  whole  drug  stores  "  and  had  been 
"treated  by  a  dozen  physicians  without  more  than  temporary  relief." 
After  questioning  her  closely  regarding  her  general  health,  1  asked 
to  be  allowed  to  examine  her  eyes,  and  found  a  simple  hyperopic  as- 
tigmatism in  each  eye,  requiring  +  .75  ax.  90  to  correct.  1  guaran- 
teed a  cure  if  she  would  wear  the  glasses  constantly.  She  followed 
my  instructions,  and  has  not  suffered  one  of  her  attacks  for  three 
years. 

After  she  had  worn  her  correction  two  months  her  huband  came 
to  see  what  could  be  done  for  him,  and  1  found  2.25  D  hyperopia,  the 
correction  for  which  he  is  still  wearing  with  great  satisfaction. 

Incidentally  the  reader  will  please  note  that  the  hyperopia  of  the 
parents  was  the  evident  cause  of  the  baby's  cross-eyes. 

Miss  D.,  aged  17,  domestic,  general  health  good;  headache  and 
menstrual  derangement,  each  successful  attempt  of  the  function  pre- 
ceded by  convulsions.  A.  +  1.75  on  each  eyeetfected  an  immediate 
and  permanent  cure. 

Young  man  of  18,  farmer,  had  headache  and  a  disordered  circu- 
lation. Went  to  an  "  oculist "  in  an  interior  city  who  prescribed  L. 
— 1.25;  R. — .50  —  .50  ax.  180.  His  trouble  increased,  and  the  country 
doctor  who  was  treating  his  blood,  concluded  his  glasses  were  wrong 
and  interfered  with  the  action  of  the  medicines.  He  came  to  me  and 
I  found  the  following  corrections:  L.  +  .25  +  .50  ax.  90;  R.  +  .25 
+  .50  ax.  90.  He  wore  the  glasses  and  continued  the  country  doctor's 
medicines,  and  was  perfectly  well  in  three  weeks. 

Master  E.,  of  Danville,  aged  14,  had  epileptic  tits.    Came  to  me 


96  OPTICAL  TRUTHS. 

wearing  —  lenses  prescribed  by  an  "oculist  "  who  was  at  that  time 
professor  of  ophthalmology  in  one  of  the  largest  medical  colleges  in 
Chicago.  1  gave  him,  L.  +  .50  +  .50  ax.  90;  R.  +  .75  +  .25  ax. 
45.  He  had  one  fit  on  the  fourth  day,  and,  when  questioned,  admitted 
he  had  left  his  glasses  off  several  hours.  He  was  given  a  lecture  and 
has  worn  the  glasses  constantly  since  without  a  recurrence  of  the 
attacks. 

Miss  L,  aged  20,  seamstress,  general  health  good,  headache,  re- 
tinal asthenopia,  muscular  insufficiency,  accommodation  weak.  She 
brought  two  pairs  of  eye-glasses  which ;had been  prescribed  "for  near 
work,  only,''  one  of  which  was  by  a  London,  Eng.,  "oculist"  who 
"  treated  "'  her  eyes  with  atropia  for  three  weeks;  the  other  was  by  a 
Chicago  optican  who  did  his  work  in  half  an  hour.  The  oculist's 
prescription  was,  L.  +  1.75  +  2.00  ax.  105;  R.  +  2.00+  .75  ax.  60. 
The  optican  gave,  L.  +  1 .00  +  2. 2 5  ax.  1 3  5 ;  R.  +  1 .00  +  .  50  ax.  60. 
Neither  pair  gave  satisfaction,  and  they  could  not  have  done  so  had 
they  been  the  proper  correction,  because,  her  nerves  were  on  a  con- 
stant strain  as  she  wore  them  for  "  near  work  only,"  according  to 
direction. 

Her  condition  has  been  told  with  the  exception  that  1  found  the 
muscular  trouble  to  be  8°  of  exophoria.  I  knew  that  was  a  temporary 
condition,  caused  by  the  depleted  nerve  force,  and  so  prescribed: 
I^  Absolute  rest  from  near  work. 

Plenty  of  sleep. 

Out-door  exercise. 

5°  prisms,  base  out  on  each  eye  for  exercise  ten 

minutes  at  a  time,  several  times  daily. 


THREE  GREAT  BLUNDERS.  97 

The  prisms  would  be  contra-indicated  in  most  cases  of  exophoria, 
and  these  were  given  more  to  treat  her  mind  than  the  muscles,  because 
she  had  formed  an  opinion  that  she  needed  medicine  rather  than 
glasses. 

After  three  days  she  returned,  and  I  found  the  rest  had  restored 
her  nerve  force  to  such  an  extent  that  her  accommodation  was  quite 
good,  and  her  muscles  now  showed  an  esophoria  of  10°.  The  orig- 
inal prescription  was  continued,  except  that  the  prisms  were  reversed. 

Three  days  later  she  showed  further  improvement,  and,  after 
three  more  days'  rest,  she  was  strong  enough  to  control  her  nerves 
while  a  satisfactory  refraction  test  was  made,  which  resulted  in  the 
following: 

L  +  .75  +  2.50  ax.  l30  ff 
R  +  2.25  ft 

She  was  directed  to  wear  spectacles,  instead  of  eye-glasses,  and  to 
wear  them  constantly.  Her  accommodation  was  sufficiently  strong  to 
read  and  do  all  near  work  without  additional  aid. 

After  another  week  of  rest  her  vision  was  f  {}  in  each  eye  and  her 
muscle  trouble  had  disappeared  entirely.  She  has  not  had  any  eye 
trouble  since. 

Miss  M.,  age  25,  health  good,  no  occupation,  headaches,  and  in- 
ability to  read  at  any  near  point.    Test: 

1  L  2V0  +  4.00  +  1.00  ax.  135  If  + 

R  /A  +  4.00  +  1.25  ax.  45  fa  + 
/  Exophoria  18°. 

Accommodation  so  weak  that  +  3.00  was  required  in  addition 
to  the  other  lenses  in  order  to  permit  her  to  read  at  l3  inches. 


98  OPTICAL  TRUTHS. 

She  was  given  the  full  correction,  directed  to  wear  it  constantly, 
take  plenty  of  sleep  so  the  nervous  system  would  have  opportunity  to 
recuperate,  and  report  in  three  weeks.  When  she  returned  vision  was 
IJ}  in  each  eye,  her  muscle  trouble  was  gone,  and  her  accommodation 
so  strong  that  she  needed  no  addition  for  reading. 

As  these  people,  and  hundreds  of  others,  have  all  recovered  with- 
out medicine,  operation,  or  prisms  (except  in  the  one  case  where 
prisms  were  given  for  the  influence  on  the  mind),  it  proves  conclu- 
sively that  the  proper  way  to  treat  all  such  cases  is  to  remove  the 
cause  entirely,  which  is  done  when  the  error  of  refraction  is  corrected. 

An  operation  upon  either  of  these  cases  would  have  been  crim- 
inal, because  the  result  would  have  been  a  needless  interference  with 
the  motion  of  the  eyeballs.  Medicines  could  not  possibly  do  any 
good  because  the  capacity  of  the  machinery  was  insufficient  to  do  the 
work.  And  "  higher  prisms"  as  they  are  sometimes  called,  by  those 
who  desire  to  express  themselves  in  riddles,  would  be  equally  criminal 
with  the  operations,  because  the  manner  of  their  application  is  such 
that  nerve  strain  is  increased. 

Conjunctivitis  is  very  common  in  hyperopes  because  the  con- 
stant action  required  from  the  ciliary  processes  causes  irritation,  which 
is  conveyed  to  the  conjunctiva  by  the  ciliary  vessels  which  perforate 
the  sclerotic  at  the  corneal  margin,  the  lids  become  feverish  and  sud- 
den contact  with  the  cold,  raw  air  of  Spring  and  Fall  causes  contrac- 
tion of  the  sphinctre  nerves  and  muscles  of  the  Meibomian  glands  in 
the  tarsal  cartilages,  and  the  sebaceous  matter  which  is  secreted  by  them 
is  forced  back  between  the  lids  and  conjunctiva,  forming  in  little 
granules  which  are  exceedingly  painful.     Medicines  have  no  place  in 


THREE  GREAT  BLUNDERS.  99 

such  cases,  except  some  antisepticlotion,  such  as  saltwater,  or  boracic 
acid  solution.  The  correction  of  the  hyperopia  removes  the  cause 
and  Nature  does  the  rest. 

1  am  well  aware  that  1  stand  alone  in  my  diagnosis  of  esophoria 
and  exophoria  by  the  tests;  also  that  many  dispute  my  claim  that 
both  eyes  are  aflfected  equally,  but  all  the  evidence  supports  my 
position. 

1  have  several  reasons,  however,  for  adhering  to  my  proposition 
that  in  muscular  insufficiencies  the  eyes  deviate  the  same  way  the 
lights  do. 

First,  the  nervous  relation  of  the  ciliary  muscles  to  the  internal 
recti.  If  the  accommodation  is  weak  the  internal  recti  must  be,  be- 
cause they  are  supplied  by  the  same  nerves.  Sometimes  a  patient 
will  show  quite  a  strong  accommodation  for  a  moment  and  yet  show 
exophoria,  but  all  that  is  necessary  to  prove  the  accommodation  is 
weak  is  to  have  the  individual  read  a  short  time. 

Second,  the  center  of  rotation  of  the  eye  being  the  pivot  upon 
which  the  visual  axis  revolves,  and  the  distance  from  that  center  to 
the  macula  being  so  infinitely  short  compared  with  the  distance  to 
the  object  observed,  a  very  slight  deviation  of  the  posterior  end 
would  cause  the  anterior  end  to  move  a  great  distance.  Now,  there 
is  a  limit  angle  to  the  deviation,  which  is  never  passed  except  in 
cross-eyes,  and  so  long  as  it  is  not  passed,  the  principal  incident  rays 
pass  the  cornea  and  cross  the  optical  axis  before  reaching  the  lens  and 
thus  strike  a  prism  base  out,  which  deflects  them  to  the  macula, 
which  sees  the  object  in  the  direction  they  came  from  last,  viz:  to- 
ward the  apex  of  that  prism. 


too 


OPTICAL  TRUTHS. 


MciculcL 


The  cut  illustrates  my  proposition.  The  candle  at  end  of  dot- 
ted line  represents  the  apparent  location  of  the  candle  in  esophoria, 
where  the  eyes  turn  in,  bringing  the  light  with  it. 

Third,  while  others  have  been  pursuing  old  methods  and  making 
repeated  failures  and  no  cures,  1  have  worked  upon  the  principle  that 
errors  of  refraction  are  the  sole  cause  of  muscular  insufficiencies,  and 
have  not  made  a  failure  in  a  single  instance. 

There  are  some  who  will  dispute  the  assertion  which  refers  to 
others  in  the  preceding  paragraph,  and  for  their  benefit  I  will  give 
an  instance  of  one  of  their  "  cures  "  which  recently  came  under  my 
observation: 

One  of  my  students,  who  found  it  difficult  to  believe  my  propo- 
sition, "because  everyone  is  against  you,"  said  he,  came  into  my 
office  a  few  weeks  after  he  had  begun  practice,  and  reported  a  phenom- 
enal cure  by  prisms.  He  said  the  case  was  treated  by  his  competitor 
but  he  had  watched  it  with  much  interest,  and  was  convinced  that 
prisms  could  not  have  been  dispensed  with  in  that  case.  I  asked  for 
the  prescription  in  full  and  he  gave  it  as  follows: 

L.  +  2.50  C  2°  prism  base  out. 
R.  +  2.50  C  2°  prism  base  out. 


THREE  GREAT  BLUNDERS.  101 

I  made  the  following  calculation:  2.50  D  hyperopia  in  each  eye, 
makes  5.00  D.  The  convergence  naturally  accompanying  2.50  D  hype- 
ropia would  be  1.25  D  in  each  eye,  making  another  2.50  D  in  both. 
The  force  required  to  be  sent  to  the  external  recti  to  prevent  the  con- 
vergent tendency  would  be  at  least  2.50  D  more,  making  a  total  nerve 
strain  of  10.  D.  Figuring  by  the  second  10  x  60  —  600  D  per 
minute;  600  x  60  =  36,000  D  per  hour;  36,000  x  16  =  576,000 
D  nerve  strain  per  day.  "  Now,"  said  I,  "  don't  you  think,  if  you 
put  on  a  +  2.50  sphere  and  thus  save  576,000  D  nerve  strain  each 
day,  she  would  regard  it  something  like  a  picnic  to  adapt  herself  to  a 
2°  prism  base  out  on  each  eye.?  "  He  whistled  softly  and  said  he 
never  gave  the  hyperopia  a  thought.  So,  it  will  be  found  that  where 
cures  have  been  effected  by  their  treatment  it  was  where  the  correc- 
tion of  the  hyperopia  really  did  it,  and  the  prisms  only  remained  a 
monument  to  stupidity. 

Fourth,  I  am  inclined  all  the  more  to  my  demonstrated  facts 
when  I  see  an  eminent  professor  in  an  Ohio  medical  college  writing: 

"  I  am  seriously  impressed  that  operative  procedures  should  be  a  dernier 
ressort,  when  all  other  means  have  failed — then  advancement  of  the  weak  mus- 
cles, instead  of  tenotomy  of  the  strong.  There  is  not  then  the  risk  of  dimin- 
ishing the  movement  of  the  eye. 

"  My  experience  has  induced  me  to  believe  that  there  is  a  very  intimate 
relation  between  spasm  of  the  ciliary  muscle  and  insufficiencies  of  the  orbital 
muscles.  I  rarely  now  make  an  examination  for  refractive  error,  without 
making  the  test  for  insufTiciencies,  and  I  have  been  surprised  at  the  frequency 
with  which  1  have  met  this  difficulty." 

Great  Scott !  Talk  about  empiricism !  Talk  about  restricting  the 
practice  of  optometry  to  the  oculists  of  Ohio,  when  one  of  the  leaders 
makes  such  confessions  of  guess-work  and    carelessness!     It  is  no 


102  OPTICAL  TRUTHS. 

longer  a  matter  of  wonder  that  the  ocuHsts  need  laws  to  force  the 
public  to  patronize  them.  I  appeal  to  the  legislature  to  come  to  their 
relief. 

Fifth,  I  am  even  more  content  to  remain  in  my  present  position 
since  the  news  comes  to  me  within  the  past  sixty  days  that  one  of  the 
most  eminent  of  all  the  New  York  ophthalmological  eminences  has 
declared  himself  "  cured  of  all  prism  nonsense." 


CHAPTER  III. 
Affections  of  the  Eyes  Commonly  Called  Diseases. 

There  are  only  two  natural  sources  of  disease:  (1),  the  blood; 
(2),  the  nerves. 

There  are  two  subdivisions  of  each,  viz.:  In  the  blood,  Hyperce- 
mia,  too  much,  or  a  congested  state,  causing  a  condition  above  nor- 
mal, feverish;  and  Aucvmia,  a  deficiency  in  quality  or  quantity,  below 
normal,  wasting.  In  the  nerves.  Paralysis,  an  interference  with  the 
circulation  of  nerve  force,  which  maybe  temporary  or  permanent; 
and  atrophy,  a  condition  of  degeneration. 

There  are  two  classifications  of  diseases  which  affect  the  eyes: 
(1),  Local;  (2),  General. 

Local  diseases  are  those  which  are  confined  to  one  district.  Gen- 
eral diseases  are  those  which  alTect  the  entire  system. 

Local  diseases  of  the  eyes  are  alTections  of  the  lids,  conjunctiva, 
lachrymal  apparatus,  cornea,  sclerotic,  choroid,  iris,  ciliary  body,  crys- 
talline lens,  vitreous  and  aqueous  humors. 

Among  the  most  common  of  these  are: 

Inflammation  of  the  lids  and  conjunctiva,  which,  speaking  truly, 
are  not  diseases  at  all,  in  most  instances.  They  are  the  effects  of  un- 
corrected errors  of  refraction.  Of  course,  after  it  reaches  the  suppu- 
rative stage  in  one  individual,  it  becomes  infectious,  and  another  may 
have  it  from  that  cause. 


104 


OPTICAL  TRUTHS. 


Growths  upon  the  lids,  such  as  chalazions,  (tumors),  and  hordeo- 
lums, (styes) ,  which  are  also  usually  the  effects  of  errors  of  refraction. 

Inversion  (turning  in)  of  the  edges  of  the  lids  from  injuries,  or 
eversion  (turning  out)  from  the  same  cause,  or  from  relaxation  of 
muscles  in  old  age. 

Keratitis,  inflammation  of  the  cornea,  and  Iritis,  inflammation  of 
the  iris,  also  from  errors  of  refraction. 

Pterygium,  a  vascular  thickening  or  growth  of  the  conjunc- 
tiva, usually  on  the  nasal  side  of  the  globe,  extending  toward  the  cornea. 
It  should  be  removed,  by  operation,  before  it  reaches  the  surface  of 
the  cornea,  else  it  will  impair  vision. 


Cataract,  an  opacity  of  the  crsytalline  lens,  due  to  traumatic  inju- 
ries or  to  senility.  When  the  opacity  has  enveloped  the  entire  lens, 
so  that  vision  is  almost  obscured,  it  is  said  to  be  "  ripe,"  and  ready  for 
extraction.  So  long  as  the  other  eye  is  good,  however,  it  is  not  ad- 
visable to  operate,  as  the  inequality  of  vision  between  the  eyes  will  be 
too  great  to  be  comfortable. 


DISEASES  OF  THE  EYE. 


105 


Opacities  of  the  humors  usually  float,  and  the  patient  will  com- 
plain of  seeing  "  black  snow."  My  experience  is  these  are  caused  by 
excessive  indulgence  in  matter  containing  too  much  sugar,  and  absti- 
nence from  salt  and  acids. 

Glaucoma,  a  disease  in  which  the  entire  globe  is  atTected,  begin- 
ning, it  is  said,  by  eminent  authorities,  with  increased  tension, 
noticeable  under  pressure;  the  patient  requires  constantly  increasing 
power  of  glasses  for  reading  on  account  of  the  diminution  of  the  power 
of  accommodation,  (the  ciliary  processes  are  supposed  to  be  the  seat  of 
the  origin  of  the  trouble),  lights  have  halos  around  them,  the  blood 
vessels  appear  to  turn  in  at  the  edges  of  the  disc  when  viewed  with 
the  ophthalmoscope,  and  the  disk  is  of  a  greenish  hue,  hence  the 
name  Glaucoma  (green).  1  have  had  one  case  which  presented  the 
so-called  deadly  characteristics  of  halos  and  the  vessels  turning  in  at 
the  edges  of  the  disk,  but,  as  the  individual  was  in  the  full  vigor  of 
manhood,  and  there  was  no  increased  tension,  his  error,  2.50  D 
hyperopia,  was  corrected  and  he  is  all  right  to-day.     Still   sees  the 


106 


OPTICAL  TRUTHS. 


halos,  but  has  a  mania  for  looking  at  lights,  which  is  enough  to  cause 
halos.  The  vessels  still  turn  in  at  the  edge  of  the  disk,  so  1  conclude 
it  is  an  unusual  case  of  "physiological  cup,"  which  even  the  glau- 
coma authorities  concede  to  be  harmless. 

General  diseases  which  affect  the  eyes  may  come  from  the 
blood  or  nervous  systems.  In  the  first  instance,  the  blood  supply 
may  be  impure,  and  obstructions  occur  in  the  circulation,  causing 
congestion  and  even  haemorrhages,  or  it  may  be  insuificient,  and 
there  be  a  lack  of  nourishment.     In  nephritis  or  diseases  of  other 


DISEASES  OF  THE  EYE.  107 

organs,  the  sympathetic  relation  between  all  parts  of  the  anatomy  exhi- 
bits itself  in  the  eyes  by  causing  inflammation  of  the  retina.  This  is 
called  retinitis.     It  is  not  a  disease,  but  a  symptom. 

Affections  from  this  source  are  observed  with  the  ophthalmo- 
scope, for  which  purpose  the  direct  method  is  the  best. 

Seat  the  patient  in  a  slightly  darkened  room,  back  to  the  light, 
which  should  be  a  round  burner,  placed  about  two  feet  distant.  Turn 
his  head  until  the  light  reflects  along  the  temple  to  the  edge  of  the 
orbit,  leaving  the  eye-ball  in  the  shadow.  Direct  his  attention  to 
some  object  straight  ahead. 

The  operator  sits  alongside  the  patient,  but  faces  the  light,  hold- 
ing the  end  of  the  handle  of  the  instrument  between  the  thumb  and 
two  first  fingers,  so  it  may  be  moved  readily,  and,  letting  the  disk 
rest  lightly  against  the  brow  and  nose  in  such  a  position  that  the 
eye  may  see  through  the  hole  in  the  mirror,  the  light  from  the  lamp 
is  reflected  from  the  mirror  into  the  pupil,  when  a  red  retlex  is  seen. 
Following  a  direct  line  toward  that  reflex  and  getting  as  close  to  the 
examined  eye  as  possible,  the  vessels  of  the  retina  will  appear;  the 
darker  ones  are  veins,  the  lighter  ones  arteries. 

Do  not  throw  the  light  into  the  eye  from  squarely  in  front, 
but  at  an  angle  of  about  thirty  degrees  from  the  optical  axis  of  the  ob- 
served eye.  Use  the  right  hand  and  right  eye  for  patient's  right,  and 
left  for  patient's  left.  Keep  the  unengaged  eye  open  if  possible,  it  will 
be  more  comfortable.  The  lenses  in  the  instrument  are  to  be  rotated 
until  one  is  found  which  affords  the  best  view  of  the  retina.  About 
—  3.00  is  required  by  beginners  for  eyes  which  are  almost  normal. 
This   is  to  offset  the    observer's   accommodation.     If   it   requires  a 


lOS 


OPTICAL  TRUTHS. 


very  strong  +  or  —  lens  to  secure  a  good  view,  the  lens  indicates 
approximately  the  amount  of  hyperopia  or  myopia,  after  deducting 
for  one's  own  accommodation. 


The  operator  should  first  familiarize  himself  with  the  appear- 
ance of  the  normal  eye,  (see  cut).     Note  the  general  field  around  the 


DISEASES  OF  THE  EYE.  109 

central  disk  where  the  vessels  meet  is  even  and  passive  in  appear- 
ance, the  edges  of  the  disk  (optic  nerve  entrance)  clear,  vessels  uni- 
formly decreasing  in  size  as  they  extend  farther  from  the  entrance,  the 
veins  darker  than  the  arteries,  which  is  proper,  because  they  carry 
the  impure  blood  back  to  the  lungs  for  purification,  while  the  ar- 
teries are  employed  to  bring  the  good  blood  out  through  the  system 
after  it  has  been  renovated.  The  light  streak  in  the  arteries  is  merely 
the  reflection  of  light  along  its  axis,  which  is  permitted  by  the  trans- 
parency of  the  blood.  Its  absence  in  the  veins  is  due  to  the  opacity 
of  the  blood  which  absorbs  the  light. 

Do  not  expect  to  see  as  much  of  the  field  at  once  as  is  shown  in 
the  cut.  An  area  about  twice  as  large  as  the  disk  is  all  that  can  be  il- 
luminated from  one  position,  but  a  slight  turn  of  the  instrument  brings 
other  parts  into  view,  and  it  is  moved  until  the  entire  retina  has  been 
examined. 

Nearly  all  beginners  rely  too  much  on  the  instrument,  and,  if 
they  do  not  see  the  entire  retina  at  the  first  attempt,  grow  discouraged. 
For  eyes  anywhere  within  3  or  4  D  of  normal,  the  blank  peep-hole  is 
used,  and  when  the  observed  eye  is  approached  at  the  proper  angle 
the  red  reflex  and  a  few  of  the  blood  vessels  will  be  seen.  Keep  the 
patient  in  that  position  and  rotate  the  lenses  until  the  one  which  gives 
the  clearest  view  is  found.  For  the  purpose  of  studying  diseases  it  is 
not  necessary  that  the  observer's  eye  be  corrected,  unless  his  error  is 
so  great  he  is  unable  to  see  anything  distinctly.  Usually  beginners 
use  their  accommodation  considerably,  so  about  —  3.00  or  —  4.00 
will  be  required  to  offset  it.  All  power  above  that  may  be  considered 
myopia  in  the  patient. 


tio 


OPTICAL  TRUTHS. 


If  the  vessels  are  congested  in  places,  as  illustrated  in  the  following 
cut,  it  is  called  a  Thrombosis,  (a  clot  of  blood),  and  is  caused  by  an 


.vr 


Embolus  (plug)  which  obstructs  circulation.  If  it  occurs  in  an  artery 
it  will  affect  vision  suddenly  and  it  is  liable  to  be  permanent.  If  it  is 
in  the  veins,  they  being  somewhat  larger,  it  may  pass  away  under 
prompt  medical  treatment,  with  possible  aid  from  massage  of  the  eye- 
ball. Or  a  haemorrhage  may  occur,  as  shown  in  the  next  illustration, 
and,  after  a  time  re-absorption  take  place,  and  vision,  which  was  lost, 
restored  again. 


Y 


DISEASES  OF  THE  EYE. 


If  the  vessels  are  thread-like,  and  the  color  of  the  arterial  blood 
is  paler  than  normal,  while  that  of  the  veins  is  dark,  but  seems  not 
to  fill  the  vessels  and  shows  a  light  streak,  and  the  general  appearance 
of  the  patient  is  corroborative  of  a  lack  of  proper  nourishment,  it  in- 
dicates disorder  of  the  generative  organs  in  females  and  functional  de- 
rangement of  the  liver  and  digestive  apparatus  generally  in  males. 

After  the  blood  vessels,  examine  the  general  field  of  the  retina, 
especially  around  the  edges  of  the  disk  for  inflammations  and  any 
other  abnormalities.     After  once  seeing  the  normal  condition  it  is  as 


112  OPTICAL  TRUTHS. 

easy  to  recognize  retinitis  as  it  is  to  know  when  the  Uds  are  in- 
flamed. The  first  appearance  is  usually  around  the  edge  of  the  disk, 
and  a  slight  degree  may  be  caused  by  a  cold,  or  over-work  from  an 
error  of  refraction,  but  the  more  intense  exhibits  mean  organic 
diseases. 

In  females  it  is  most  commonly  from  ills  incident  to  their  sex, 
and  in  males  the  great  majority  are  renal  troubles.  The  commonest 
cause  of  female  ills  is  hyperopia,  and  ignorance  of  the  functions  of 
their  procreative  organs  and  how  to  care  for  them. 

It  is  to  be  hoped,  for  the  sake  of  posterity,  that  the  higher  educa- 
tion of  daughters,  and  sons  too,  will  soon  include  a  thorough  know- 
ledge of  every  function,  and  common  sense  enough  to  care  for  them. 
It  would  result  not  only  in  a  higher  state  of  physical  health,  but  in 
moral  elevation  as  well. 

The  commonest  cause  of  kidney  troubles  in  males,  is  excessive 
use  of  malt  liquors,  which  not  only  overload  the  organs  by  the  great 
quantities  taken,  but  the  chemicals  used  in  their  preparation  have 
the  effect  of  reducing  their  capacity. 

In  hyperopia  the  constant  accommodative  effort  causes  a  sym- 
pathetic contraction  of  the  sphincter  muscles  throughout  the  body,  (and 
it  must  be  remembered  every  opening  in  the  body,  large  or  small,  is 
surrounded  by  such  a  muscle),  among  them  that  of  the  uterus,  thus 
interfering  with  the  menstrual  function.  This  sets  up  a  disturbance 
which  is  reflected  back  to  the  eye,  causing  further  contraction  of  the 
muscles  there,  even  to  those  surrounding  the  optic  nerve  at  its  en- 
trance, with  the  result  that  the  arterial  circulation  is  cut  off  so  blood 
cannot  enter  the  eye,  venous  circulation  is  impeded  so  blood  cannot 


-^v 


\ 


DISEASES  OF  THE  EYE. 


113 


pass  out,  and  the  field  around  the  edge  of  the  disk  becomes  so  irritated 
that  the  disk  appears  hke  a  splash  of  cheap  whitewash,  tinted.  The 
cut  was  drawn  from  such  a  case. 


The  Creator  evidently  intended  only  water  to  be  used  as  a 
beverage,  else  there  would  have  been  an  occasional  river  of  beer  or 
some  other  liquid. 

The  ophthalmoscopic  appearance  is  very  much  like  that  shown 
in  the  last  illustration.  It  is  diffused  over  a  larger  field  and  does  not 
appear  quite  so  intense,  except  in  advanced  stages,  when,  in  addition 
to  the  inflammation,  irregular-shaped  oedemic  patches  appear  from 


114  OPTICAL  TRUTHS. 

which  the  circulation  has  been  cut  o1^"  by  the  swelling".  This  condi- 
tion is  said  to  be  a  sure  indication  of  Bright's  disease.  If  these 
appear  black,  as  they  will  when  the  degenerated  tissue  disappears, 
showing  the  pigment  layer,  it  is  safe  to  predict  early  death.  If  your  pre- 
diction fails,  the  patient  is  pleased,  and  if  it  is  fulfilled  your  reputation 
is  enhanced. 

There  are  many  diseases  which  will  cause  retinitis.  I  have  only 
mentioned  these  because  of  their  frequency.  So,  after  finding  the 
condition,  consult  the  patient  to  find  the  cause.  Hear  his  story  pa- 
tiently,ask  questions, probe  family  history,  etc.,  get  the  facts,  and  you 
cannot  possibly  fail  in  your  diagnosis,  if  you  do  in  treatment. 

If,  after  careful  examination  of  the  vessels  and  tissue  nothing  ab- 
normal is  found,  proceed  with  the  visual  tests.  If  vision  is  poor  and 
cannot  be  improved  to  approximately  normal,  it  must  be  the  nerves 
which  are  affected.  There  is  no  other  source  left.  If  vision  was  lost 
suddenly,  it  is  paralysis,  and  the  application  of  electricity  together 
with  constitutional  treatment  and  rest  may  restore  it.  If  sight  passed 
away  gradually,  it  is  atrophy,  and,  while  the  progress  of  the  disease 
may  be  arrested,  the  dead  nerves  can  never  be  revived. 

The  commonest  causes  of  nerve  troubles  are  excessive  use  of 
spirituous  liquors  and  tobacco,  diseases,  such  as  scarlet  fever,  measles, 
typhoid,  la  grippe,  and  their  ilk.  But,  as  cited  in  reference  to  other 
atfections,  the  specific  cause  may  be  located  in  any  given  instance  by 
questioning  the  patient. 

Treatment. 

First.  Having  discovered  the  cause  of  trouble,  if  it  be  from  an 
acquired  habit,  such  as  liquor,  tobacco,  etc.,  order  it  stopped.     If  it 


DISEASES  OF  THE  EYE.  115 

be  from  a  natural  habit,  such  as  eating  and  drinking  the  foods  neces- 
sary to  sustain  Hfe,  or  from  excessive  sexual  indulgence,  order  it  reg- 
ulated. 

Second.  Correct  whatever  errors  of  refraction  are  found,  and 
direct  the  patient,  in  plain  terms,  how  to  wear  it,  giving  simple 
reasons  therefor. 

Third.  If  you  are  not  a  physician,  and,  in  your  judgment, 
medical  treatment  is  needed,  see  that  it  is  secured.  The  patient's  family 
physician  is  the  proper  one  to  treat  such  cases,  and  it  is  right  for  you 
to  send  him  a  note  or  give  him  an  oral  statement  of  the  conditions 
you  have  found. 


CHAPTER  IV. 

Anatomy  and  Physiology  of  the  Eye  and  Its  Appendages. 

The  orbits  are  the  hollow  cavities  in  the  skull  which  contain  the 
eyeballs,  and  afford  protection  from  injury.  They  are  lined  with  a 
fatty,  fibrous,  cartilaginous  cushion  called  the  Aponeurosis,  from 
which,  in  the  posterior  portion  arise  the  muscles  which  hold  the  eye  in 
position. 

The  lids  perform  the  office  of  shutters  to  the  orbits  excluding 
light  and  protecting  the  eyes  from  dust,  etc. 

The  conjunctiva,  or  lining  membrane  of  the  lids,  extends  over 
the  anterior  surface  of  the  globe,  and,  being  lubricated  from  the  Lach- 
rymal Glands,  affords  two  smooth  surfaces  which  prevent  friction  in 
winking. 

The  eye-ball  is  spherical  in  form,  with  a  projecting  segment  of  a 
smaller  sphere  on  its  anterior  surface,  by  means'of  which  the  refract- 
ive properties  are  increased,  so  that  light  will  be  focused  on  the  retina. 
It  is  composed  of  three  principal  layers:  (1),  the  sclerotic  and  cornea; 
(2),  the  choroid,  iris,  and  ciliary  processes;  (3),  the  retina.  These 
layers  form  two  principal  cavities;  (1),  behind  the  crystalline  lens, 
filled  with  vitreous  humor;  (2),  in  front  of  the  lens,  filled  with 
aqueous  humor.  The  iris  is  suspended  in  the  front  cavity  dividing 
it  into  two  chambers,  the  anterior  and  posterior,  which  are  connected 
by  the  opening  in  the  iris  called  the  pupil. 


118 


OPTICAL  TRUTHS. 


ANATOMY  OF  THE  EYE.  119 

The  cut  illustrates  the  relative  positions  of  the  eyes,  and  the 
source  of  their  nerve  supply,  showing  why  pains  in  the  eyes  are  always 
referred  to  the  back  of  the  head.  The  sclerotic,  choroid  and  retina  are 
shown  in  their  respective  locations  as  the  outer,  middle  and  inner 
layers  of  the  eye-ball.  The  dark  lines  represent  the  internal  and  ex- 
ternal recti  muscles,  and,  posteriorly,  is  shown  the  cartilaginous  sub- 
stance where  all  the  muscles  of  the  globe  have  their  origin. 

The  globe  and  its  contents  form  what  is  termed  the  dioptric 
system. 

The  dimensions  of  the  eye  are,  antero-posterior  diameter,  .95 
inch;  horizontal,  .92  inch;  vertical,  .90  inch.  The  optical  axis  is  an 
imaginary  line  connecting  the  anterior  and  posterior  poles,  which  are 
the  geometric  centers  of  the  cornea  and  the  retina.  The  visual  axis  is  an 
imaginary  line  from  the  macula  to  the  object  observed,  and  crosses  the 
optical  axis  at  the  optical  center  of  the  lens,  so  that  in  looking  at  dis- 
tant objects  the  two  eyes  receive  the  same  image  without  any  effort  at 
convergence. 

The  sclerotic  is  a  dense,  fibrous  membrane,  without  nerves,  and 
with  few  blood-vessels.  It  encloses  about  four-fifths  of  the  globe,  and 
the  cornea  the  remainder.  The  latter  is  transparent  and  is  of  cellular 
structure;  has  nerves  but  no  blood-vessels,  except  at  the  margin, where 
there  is  a  narrow  space  plentifully  supplied  from  capillaries  from  the 
ciliary  processes.  The  sclerotic  and  cornea  form  a  layer  of  protection 
to  the  more  delicate  inner  coats. 

The  choroid,  (sometimes  called  the  uveal  tract),  is  a  vascular 
membrane,  dark  brown  in  color,  and  is  attached  to  the  sclerotic  at  the 
ciliary  processes  and  at  the  optic  nerve  entrance.  It  is  the  layer  of  nour- 


120  OPTICAL  TRUTHS. 

ishment,  carrying^  the  blood  and  nerve  supply  of  the  eye.  The  ciliary 
processes  are  folded  elongations  of  the  anterior  part  of  the  choroid  in 
which  are  located  the  suspensory  ligaments  and  sphincter  muscles 
which,  with  the  zone  of  Zinn  and  crystalline  lens,  complete  the  mechan- 
ism of  accommodation.  The  iris  is  a  continuation  of  the  choroidal 
coat  and  forms  a  curtain  which  regulates  the  amount  of  light  admitted 
to  the  interior.  It  is  formed  form  a  combination  of  radiating  and  cir- 
ular  muscles,  and  is  colored  by  a  layer  of  pigment  cells,  continuous 
with  that  pigmentary  lining  of  the  choroid  which  receives  the  light 
after  it  has  passed  the  retina,  on  the  same  principal  that  the  earth  is 
utilized  by  telegraphers  to  "ground  "  electric  currents  to  prevent  burn- 
ing out  of  instruments. 

The  retina  is  the  optic  nerve  expanded  into  a  membrane.  Its 
function  is  to  receive  the  incident  rays  and  telegraph  the  impressions 
to  the  brain.  It  is  composed  of  many  layers,  and  is  most  highly  sen- 
sitive in  that  portion  in  the  vicinity  of  the  posterior  pole  where  inci- 
dent rays  from  the  pupillary  space  form  images.  At  the  optic  nerve 
entrance  there  is  no  sensibility,  and,  under  the  ophthalmoscope  it 
appears  as  a  disk,  almost  white,  and  is  seen  a  little  to  the  nasal  side  of 
the  posterior  pole.     It  is  the  "  blind-spot." 

The  aqueous  humor  is  a  transparent  fluid,  with  a  specific  gravity 
about  equal  to  distilled  water,  and  fills  all  the  space  in  front  of  the 
crystalline  lens.  It  is  a  glandular  secretion,  related  to  the  lachrymal 
apparatus,  and  if  the  cornea  is  punctured,  allowing  it  to  escape,  it  will 
refill  the  space  in  a  few  hours. 

The  crystalline  humor,  or  lens,  is  a  substance  of  peculiar  forma- 
tion.    Although  seemingly  a  liquid,  it  is  of  a  striated  composition  of 


ANATOMY  OF  THE  EYE.  121 

several  layers  and  conditions  of  refracting  and  dispersing  powers. 
The  combination  forming  an  achromatic,  or,  rather  an  aplanatic 
(meaning  both  spherical  and  chromatic  aberration  are  corrected)  lens. 
It  is  most  probable  here  is  the  seat  of  color  blindness,  when  the  aplan- 
atism  is  not  complete.  The  lens  is  enclosed  in  a  capsule  and  this  is 
attached  to  a  tubular  structure,  the  zone  of  Zinn,which  is  attached  to  the 
ciliary  processes.  The  lens  has  a  natural  tendency  to  contract  peri- 
pherally, and  expand  along  its  antero-posterior  axis,  making  it  more 
convex,  thus  increasing  its  refractive  power.  This  is  assisted  by  a 
similar  tendency  on  the  part  of  the  zone  of  Zinn,  but  the  suspensory 
ligaments,  having  greater  contracting  power,  pull  outward  on  the  com- 
bination and  hold  the  lens  in  its  thinnest  form.until  there  is  a  demand 
for  more  convexity  of  the  dioptric  system,  when  the  sphincter  muscle 
receives  an  impulse  from  the  third  nerve  and  contracts,  like  a  watch 
spring,  thus  overcoming  the  suspensory  muscles  to  whatever  extent  the 
occasion  demands.  It  is  the  loss  of  this  impulse  which  is  called  pres- 
byopia. 

The  vitreous  humor  fills  the  main  globe  of  the  eye  and  holds  the 
choroid  and  retina  in  close  contact  with  the  sclerotic.  It  is  a  trans- 
parent gelatin-like  substance,  and  is  enclosed  by  a  delicate  membrane 
called  the  hyaloid,  which  forms  a  lining  to  the  retina,  and  in  case  of 
haemorrhages  of  retinal  vessels,  is  useful  in  holding  the  extravasated 
blood  in  the  tissue  affording  opportunity  for  re-absorption. 

The  blood  supply  of  the  eye  comes  from  the  ophthalmic  artery, 
which  is  a  branch  of  the  internal  carotid,  from  the  common  carotid, 
from  the  arch  of  the  aorta.  There  are  two  main  veins,  the  superior 
and  inferior  ophthalmic,  which  empty  into  the  cavernous  sinus,  and 
also  connect  with  the  veins  of  the  face,  thus  allowing  free  circulation. 


122  OPTICAL   TRUTHS. 

The  muscles  of  the  eye-ball  are  six:  four  recti,  the  superior,  in- 
ferior, internal  and  external,  and  two  oblique  or  pulley  muscles,  the 
superior  and  inferior,  which  pass  along  the  nasal  side  to  a  ligament, 
thence  over  and  under  the  globe.  The  function  of  the  muscles  is  to 
rotate  the  eye-ball  in  its  socket. 

The  muscles  of  the  lids  are  the  orbicularis  palpebrarum,  corru- 
gator  supercillii,  tensor  tarsi,  and  levator  palpebrce. 

The  cartilages  of  the  lids  are  the  superior  and  inferior  tarsal. 
They  give  form  and  support  to  the  lids.  The  outer  angle  of  each  is 
attached  to  the  malar  bone  by  the  external  palpebral  or  tarsal  ligament, 
while  the  inner  angles  terminate  at  the  commencement  of  the  lacus 
lachrymalis,  (the  space  next  the  nose  where  the  tears  find  entrance 
to  the  nasal  duct),  and  are  fixed  to  the  margin  of  the  orbit  by  the 
tendo  oculi. 

The  Meibomian  glands  are  located  in  the  tarsal  cartilages,  and 
correspond  in  length  to  the  width  of  those  cartilages.  They  are 
more  numerous  in  the  upper  than  in  the  lower  lids  and  secrete  a  se- 
baceous matter  which  is  exuded  upon  the  free  margins  of  the  lids, 
preventing  adhesion  when  they  are  closed. 

The  lachrymal  glands  are  situated  at  the  upper  outer  angle  of 
the  orbits  and  their  secretions  are  carried  away  by  many  small  ducts 
which  lubricate  the  conjunctiva  and  pass  away  through  the  lachrymal 
canals  and  nasal  duct  at  the  inner  angle  (or  canthus). 

The  nerves  of  the  eyes  are  the  2d,  3d,  4th,  6th,  and  part  of  the 
5th  cranial.  The  2d  alTords  the  sense  of  sight,  the  3d  operates  all 
muscles  except  the  superior  oblique  and  external  recti,  which  are  sup- 
plied respectively  by  the  4th  and  6th. 


CHAPTER  V. 
Mydriatics  and  Myotics— Drugs  which  acton  the  Accommodation, 

Mydriatics  are  drugs  which  paralyze  the  accommodation.  Those 
commonly  used  are:  (1),  Atropine,  an  alkaloid  of  Atropa-Belladonna, 
or  Deadly  Night-shade;  (2),  Homatropine,  a  product  of  Atropine; 
(3),  Duboisine,  from  Duboisia  Myoporoides;  (4),  Hyoscamine,  or 
Scopolamine,  from  Scopolia  J aponica;  (5),  Daturine,  from  Daturia 
Stramonium;  (6),  Gelsemine,  from  Gelsemium  Sempervirens;  (7), 
Cocaine,  from  Erythroxylon  Coca. 

Those  in  most  common  use  are  Atropia-sulphate  and  Scopola- 
mine. They  are  used  in  solution  of  2  to  4  per  cent.  The  objections 
to  their  use  are:  (1),  the  length  of  time  required  to  secure  complete 
mydriasis;  (2),  the  discomfort  to  the  patient  from  the  effect  on  the 
general  system  which  it  enters  via.  the  tear-duct  through  the  nose  and 
throat;  (3),  it  does  not  keep  longer  than  a  couple  of  weeks;  (4),  the 
dose  is  unavoidably  inaccurate  as  to  strength. 

The  Homatropine  combined  with  Cocaine,  and  put  up  in  gelatin 
disks  is  the  most  satisfactory  of  all  mydriatics,  because,  (1),  the  ac- 
curacy of  the  dose;  (2),  it  keeps  indefinitely;  (3),  it  acts  quickly;  (4), 
there  is  absolutely  no  danger  in  its  use. 

The  disks,  as  put  up  by  Wyeth  &  Bro.,  and  kept  by  all  optical 
houses,  are  in  bone  boxes  each  containing  fifty  disks.  The  stock 
numbers  of  the  ones  most  used  are: 


124  OPTICAL  TRUTHS. 

No,  338  Homatropine  and  Cocaine,  5V  grain  of  each  in  each 
disk.  One  disk  in  each  eye,  under  the  upper  lid,  (which  should  be 
everted  and  the  disk  placed  on  the  conjunctiva,  so  it  will  be  above  the 
apex  of  the  cornea),  will  smart  slightly  for  a  few  moments,  during 
which  time  the  eyes  should  be  kept  closed;  after  twenty  minutes  the 
pupils  will  dilate,  and  in  about  one  hour  the  patient  will  be  unable  to 
read  ordinary  print  at  any  distance.  The  effects  pass  away  in  about 
twelve  to  twenty-four  hours,  and  there  are  none  of  the  after-effects 
which  are  so  common  in  the  use  of  the  solutions. 

No.  336  Homatropine  gi^  grain,  is  used  as  the  other;  dilates  the 
pupil  for  ophthalmoscopic  examinations,  and  may  be  used  on  old 
people  to  enable  the  physician  to  examine  cataracts  in  order  to  ascer- 
tain their  condition. 

No.  323  cocaine  muriate,  is  a  local  anaesthetic,  used  to  deaden 
the  conjunctiva  while  foreign  bodies  imbedded  therein  are  removed. 
Takes  effect  in  about  six  minutes,  and  passes  off  in  about  twenty  min- 
utes; dilates  pupil  for  several  hours.  As  soon  as  smarting  ceases  after 
inserting,  go  to  work  on  the  object. 

Myotics  produce  artificial  stimulation  to  the  sphincter  muscles. 
Those  most  used  are  Eserine,  Calabarine  and  Physostigmine,  all 
Alkaloids  of  Calabar  Bean. 

No.  33 1  Eserine  yoVo  grain  to  the  disk  is  used  as  the  others,  ex- 
cept for  the  opposite  effect.  In  some  instances  of  iritis  with  spasm 
of  accommodation  there  is  danger  of  the  iris  adhering  to  the  lens,  and 
if  it  does,  Atropine  is  used  to  pull  it  loose,  alternating  it  with  Eserine 
to  prevent  mutilation  of  the  membranes.  Again,  in  myosis,  or  en- 
larged pupil  from  inaction  of  the  sphincter  muscles  of  the  iris,  Es- 
erine is  used  in  the  effort  to  stimulate  it  to  action. 


CHAPTER  VI. 

Color-Blindness^  and  a  Comparison  of  the  Tests  Therefor. 

This  subject  is  one  which  has  been  widely  studied  and  writ- 
ten upon;  but,  as  yet,  no  one  has  reached  conclusions  susceptible 
of  demonstration  with  satisfaction  to  all  and  the  etiology  is  as  obscure 
as  that  of  the  "  expression"  of  the  eyes. 

One  theory  is  that  the  retina  possesses  three  sets  of  color- per- 
ceiving elements,  viz:  those  for  red,  green  and  blue,  or  violet. 

Another  is  that  there  exists  in  the  retina  three  ditferent  visual 
substances,  viz:  red-green,  blue-yellow,  and  white-black.  It  is  claimed 
that  one  color  of  each  pair  is  used  up  by  the  process  of  dissimilation 
and  the  other  is  produced  by  a  sort  of  creative  process  called  assimila- 
tion, that  white  corresponds  to  the  process  of  dissimilation,  and  black 
to  the  process  of  assimilation;  that  for  the  two  other  pairs  it  cannot 
be  said  which  color  represents  either  process. 

Another  proposition  is  that  we  know  everything  by  comparison 
with  some  other  thing — a  large  man  by  comparison  with  what  we 
know  to  be  the  average  size,  a  red  color  by  comparison  with  yellow, 
a  black  by  comparison  with  a  white. 

All  of  these  appear  to  me  to  be  the  same  idea,  expressed  dif- 
ferently, the  latter  being  rather  more  intelligible  than  the  others.  But 
just  why  or  how  the  retina  is  able  to  produce  the  particular  color  for 
comparison  is  the  unexplained  feature.     I  know  they  say,  and  prove, 


126  OPTICAL  TRUTHS. 

that  the  presence  of  one  color  leaves  an  after-effect  which  produces 
the  other,  and  upon  this  ground  their  theory,  but  why  does  it  do  so? 

The  series  of  colored  plates  on  the  following  pages  illustrate  the 
facts.     The  reason  for  their  existence  is  not  so  clear  by  any  means. 

1  have  a  theory  which  1  will  give  for  what  it  is  worth. 

It  is  well-known  that  crown  and  flint  glass,  with  approximately 
the  same  index  of  refraction,  have  decidedly  different  indices  of  dis- 
persion, the  last  named  having  twice  as  much  of  the  dispersive  quality 
as  the  first.  All  high  grade  mathematical  instruments  utilize  this  prop- 
erty to  overcome  spherical  and  chromatic  aberration.  Before  the  dis- 
covery of  the  peculiarity  of  flint  glass  it  was  impossible  to  make  lenses 
of  higher  magnifying  power  than  about  twenty-five  diameters  because 
of  the  diffusion  of  color  over  the  observed  field.  In  the  chapter  on 
"  Laws  of  Refraction  "  the  illustration  was  used  which  is  here  repro- 
duced, and  it  was  stated  that  it  exhibited  the  principle  upon  which 
achromatic  and  aplanatic  lenses  are  made. 


'    The  manner  in  which  it  is  utilized  is  as  follows: 

A  lens  of,  say,  two  inches  focus  is  desired,  and  a  biconvex  crown 
glass  of  40  D  or  1-inch  focus  is  taken  for  the  nucleus,  on  one  side  is 
cemented  a  concave  meniscus,  or  periscopic-concave  flint  glass  lens  of 
20.  D  which  neutralizes  half  of  the  refractive  power  of  the  other  and 


COLOR-BLINDNESS.  127 

all  of  its  dispersive  power,  thus  securing  a  +  20.  D  or  2-inch  focus, 
without  any  dispersion.  When  it  was  found  there  was  still  a  dif- 
ficulty from  the  extreme  edge  rays  focusing  just  a  little  sooner  than 
those  passing  the  main  body  of  the  lens,  preventing  a  distinct  image 
being  secured,  it  was  obviated  by  dividing  the  tlint  glass,  putting  — 
10.  D  on  each  side  of  the  crown. 

Now,  all  authorities  agree  that  the  crystalline  lens  is  constructed 
upon  the  same  principle,  and  I  believe  it  was  done  for  the  same 
purpose,  for  1  have  not  found  a  single  case  of  true  color-blindness 
in  which  I  was  able  to  secure  |f  vision  and  they  invariably  had  great 
errors  of  refraction. 

One  may  have  an  error  of  refraction  without  color-blindness,  be- 
cause the  composition  of  the  lens  may  be  normal.  And  one  may  be 
color-blind  from  an  abnormal  consistency  of  the  lens,  yet  have  no 
error  of  refraction.  Still  his  acuteness  of  vision  will  be  below  normal, 
and  nothing  will  bring  it  up  to  the  standard. 

I  am,  therefore,  of  the  opinion  that  the  test  for  color-blindness  is 
not  complete  without  a  test  for  errors  of  refraction,  and  if  I  find  a 
seeming  deficiency  in  the  color- sense,  yet  vision  can  be  brought  to  f^, 
I  pronounce  it,  not  color-blindness,  but  color-ignorance.  A  number 
of  experiments  have  convinced  me  that  all  such  persons  can  be  ed- 
ucated to  match  colors  as  well  as  anyone. 

Of  the  methods  of  testing  the  color-sense  the  ancient  one  by 
Prof.  Holmgren,  of  comparing  skeins  of  worsted  and  the  modern 
one  devised  by  Prof.  Rumble,  are  the  only  two  in  general  use. 

Of  these  two,  the  newer  one  is  unquestionably  superior  because 
it  can  be  used  with  equal  facility  day  or  night,  while  the  other  is 
practicable  only  in  good  day  light. 


128 


OPTICAL  TRUTHS. 


The  accompanying  cuts  show  front  and  back  views  of  the  test, 
which  is  mounted  upon  a  card  S}i  x  12  inches  in  size,  and  of  heavy, 
durable  material.  The  colors  are  arranged  on  two  revolving  disks,  and 
are  of  celluloid.  The  test  colors,  light  green,  rose  and  red,  are  on  the 
small  disk,  together  with  white.  Three  shades  each  of  green,  rose,  red, 
blue,  orange,  purple  and  gray,  are  attached  to  the  large  disk,  which  is 
revolved  slowly,  presenting  the  several  shades,  which  are  numbered, 
at  the  lower  opening  of  the  two  shown  in  the  upper  cut  for  compar- 
ison with  the  test  color  shown  at  the  upper  opening. 


TEST    FOR    COLOR    BLINDNESS. 


001L.0TI   I^"CnL^^E3FlJ5. 


Oraorc.  LiRfa' 
Purple,  LiBhi 


(fat      (2:»> 


y 

DIRECTIONSi                                                             \J 

/     ..Zfii^r^flL 

hetnrt,-  0  window  or  arlirioal   tigbl.   tf  artificial  the  llshi        \ 

aboui   icn  Itut  dlMaoii  I'uro  KmatI  dink  until  light  grMia  i* 
to  name    (he   coh.r.    F»ilBfc  riignKICH  ealoi^  blinitncsn. 

':;ir.;r^r«,':.".'„ 

\i::j:r,'-^:kr.n°\rJ^!^uiT::"^vNJtL':?s:i 

4,     Second  Te»I 

SOUD  BV  ALL,  JOBBERS. 

COLOR-BLINDNESS. 


129 


The  following  form  is  used  by  many  railroads  for  recording  the 
results  of  the  test.  The  name  of  the  color  submitted  is  not  recorded 
in  the  first  column  until  the  test  is  over  and  patient  gone. 

Name  of  Patient,  C.  E.  DAVIS. 


Test  Color  Submitted. 

Name  Given. 

NDMBER  SELECTED  TO  MATCH. 

GREEN 

ROSE 

RED 

GREEN 

RED 

RED 

12,  16,  11,  6,  3,  2,  21. 
10,   8,   7,  22,   18,  14. 
18,   14,  10,  4. 

Reference  to  the  Chart  under  head  "  Color  Numbers  "  shows  2, 
16  and  6  are  green,  while  11,3,  and  21  are  blue,  and  12  is  purple. 

In  the  second  test  "rose  "  was  called  "  red  "  and  of  the  colors 
matched  with  it  10  and  18  are  red,  7  is  orange,  and  8,  14  and  22  are 
rose. 

In  the  third  test  he  named  color  properly  and  matched  them 
without  fault,  except  that  he  added  dark  rose  to  the  collection. 

According  to  article  6  of  "  Directions"  this  was  a  case  of  violet- 
blindness. 

In  cases  where  there  is  a  reasonable  doubt  of  true  color-blindness, 
a  statement  should  be  made  to  that  eiTect  in  the  report,  so  that  if  the 
individual's  pecuniary  interests  are  involved  he  may  have  opportunity 
to  practice  with  colors,  and,  if  possible,  thus  remove  the  obstacle  in 
the  way  of  his  employment.  Careless  examiners  often  commit 
grave  injustice  to  persons  in  the  employ  of  corporations,  where  a 
good  color-sense  is  necessary,  and  such  carelessness  deserves  as  severe 
punishment  as  would  follow  the  passing  of  a  color-blind  person. 


130  OPTICAL  TRUTHS. 

The  cuts  on  the  following  pages  are  a  preliminary  test  for  color- 
blindness, and  show  the  rapidity  of  color  perception  in  a  manner  be- 
yond question.  The  effects  to  the  eye  with  normal  color  sense  will 
be  as  follows: 

Look  at  the  eye  of  the  figure  for  a  short  time,  say  half  a  minute, 
then  cover  it  with  a  blank  sheet  of  heavy  white  paper,  and  fix  the 
gaze  on  one  spot,  and  its  complementary  color  will  appear:  If  the 
figure  observed  is 

Black,  white  will  appear; 

Red,  green  will  appear; 

Green,  red  will  appear; 

Yellow,  blue  will  appear; 

Blue,  yellow  will  appear. 


COLOR-BLINDNESS. 


131 


APPENDIX. 
A  Quiz  Compend,  Embracing:  the  Principal  Points  of  Practice. 

Question.    What  is  force? 

Answer.     It  is  that  which  causes  or  arrests  motion. 

Q.     What  is  Hght? 

A.      It  is  a  force,  positive  and  negative. 

Q.     How  many  kinds  are  there? 

A.     Two,  natural  and  artificial. 

Q.     What  is  meant  by  refraction? 

A.  The  word  "  refraction  "  means  "to  break."  The  refraction 
of  light  is  the  deviation  in  its  course  a  ray  suffers  in  passing  obliquely 
from  one  transparent  medium  to  another  of  different  density. 

Q.     What  is  meant  by  "  index  of  refraction?" 

A.  It  is  the  comparative  rate  of  speed  at  which  a  ray  travels  in 
mediums  of  dit^erent  density. 

Q.  Why  do  we  take  air  as  our  standard  of  measurement  of  re- 
fraction ? 

A.  Because  it  is  the  rarest  medium,  and  is  the  one  through 
which  all  light  comes  to  us. 

Q.     What  are  three  principal  laws  of  refraction? 

A.  First,  the  deviation  oblique  rays  suffer.  Second,  a  ray  pass- 
ing a  prism  is  broken  toward  the  base.     Third,  in   order  to  utilize 


134  OPTICAL  TRUTHS. 

refraction  for  optical  purposes,  we  must  have  curved  surfaces  in  order 
to  get  foci . 

Q.    What  three  things  always  accompany  refraction? 

A.     Reflection,  dispersion  and  absorption. 

Q.     What  three  things  are  necessary  to  illustrate  refraction? 

A.  Two  transparent  mediums  of  different  density  and  an 
oblique  ray. 

Q.     What  is  a  nodal  point? 

A.     A  center  of  curvature. 

Q.     What  is  a  prism?  . 

A.    A  wedge,  of  some  transparent  substance. 

Q.     How  are  prisms  utilized  in  the  formation  of  lenses? 

A.  They  are  used  in  multitudinous  quantities,  of  different  an- 
gles, and  are  arranged  around  a  central  point  for  sphericals,  bases 
toward  that  point  for  +,  and  away  from  it  for  — ,  in  such  order  that 
the  result  is  a  spherical  curvature.  For  cylinders  they  are  arranged 
on  either  side  of  a  line,  so  as  to  form  either  +  or  —  cylindrical  curv- 
atures 

Q.     How  many  kinds  of  lenses  are  there? 

A.     Two,  convex  and  concave,  (+  and  — ). 

Q.    What  are  the  general  forms  of  lenses? 

\.     Spherical  and  cylindrical. 

Q.    What  class  of  lenses  form  images? 

A.     Spherical. 

Q.     Locate  the  nodal  points  of  a  lens? 

A.  They  are  the  points  upon  the  principal  axis  where  the  sec- 
ondary axial  rays  would  cross  did  they  not  suffer  refraction . 


APPENDIX.  135 

Q.     Locate  the  optical  center  of  a  lens? 

A.  It  is  the  point  on  the  principal  axis  where  the  refracted  sec- 
ondary axial  rays  cross. 

Q.  Locate  the  principal  foci  of  a  +  spherical  lens,  and  state  if 
they  are  movable  or  fixed.? 

A.  They  are  the  points  on  the  axis,  on  either  side  of  the  lens, 
where  rays  are  focused  which  were  parallel  to  the  axis  on  the  oppo- 
site side.    They  are  fixed. 

Q.  Locate  the  conjugate  foci  of  a  +  spherical  lens,  and  state  if 
they  are  movable  or  fixed.'' 

A.  They  are  the  points  on  the  principal  axis,  on  either  side  of 
the  lens,  where  the  object  and  its  image  are  respectively  located.  They 
are  movable,  the  position  of  the  image  being  governed  by  the  location 
of  the  object,  hence  the  name  "  conjugate "  which  means  "yoked 
together." 

Q.  What  class  of  lenses  have  their  conjugate  foci  on  the  same 
side  of  the  lens.^" 

A.    Concave  ( — )  spherical, 

Q.     What  class  of  lenses  form  images  reversed.? 

A.     Convex  (+)  spherical. 

Q.    Why  is  this  so.? 

A.  Because  the  secondary  axial  rays  always  cross  the  principal 
axis  at  the  optical  center,  and  the  law  of  conjugate  foci  brings  rays 
from  a  point  on  one  side  of  the  lens,  back  to  a  point  on  the  other 
side,  on  a  direct  line  with  the  starting  point  and  the  optical  center  of 
the  lens. 

Q.  How  many  ways  are  there  of  finding  the  location  of  the 
second  conjugate  focal  point.? 


136  OPTICAL  TRUTHS. 

A.  Two,  one  practical  and  the  other  theoretical.  First  find  the 
refracting  power  of  the  lens,  draw  a  plane  through  the  first  principal 
focal  point,  than  draw  a  line  from  the  object,  on  the  axis,  to  the  lens 
at  some  distance  from  the  axis  toward  the  edge,  then  draw  a  line  from 
the  point  where  the  first  line  crossed  the  focal  plane,  through  the  ob- 
tical  center  of  the  lens,  then  continue  the  first  line  beyond  the  lens 
parallel  to  the  second  until  it  touches  the  principal  axis;  this  point  is 
the  second  conjugate  focus.  The  rule  to  calculate  this,  is:  The  first 
conjugate  focal  distance  and  the  focal  length  of  the  lens  being  given, 
multiply  them  together  and  divide  the  product  by  the  difference  be- 
tween them;  the  result  will  be  the  second  conjugate  focal  distance. 

Q.  At  what  distance  from  a  lens  must  an  object  be  placed  in 
order  that  its  image  will  be  formed  at  the  same  distance  on  the  other 
side,  and  what  will  be  their  relative  size? 

A.     At  twice  the  focal  length,  and  they  will  be  of  equal  size. 

Q,     How  many  principal  axes  has  a  lens? 

A.     One,  the  line  from  one  nodal  point  to  the  other. 

Q.     How  many  secondary  axial  rays  are  there? 

A.  All  rays  which  cross  the  principal  axis  at  the  optical  center 
are  secondary  axial  rays,  and  they  are  innumerable. 

Q.  What  is  the  peculiar  difference  between  principal  and  sec- 
ondary axial  rays? 

A.  The  principal  suffer  no  refraction,  while  the  secondary  do; 
it  is  so  little,  however,  it  is  not  considered  in  calculation, 

Q.    What  is  the  advantage  of  the  metric  system  of  numbering? 

A.    It  simplifies  calculations  to  mere  addition  and  substraction 

Q.    What  is  a  toric  lens? 


APPENDIX.  137 

A.  One  in  which  the  sphere  and  cyHnder  are  both  ground  on 
one  surface, 

Q.     What  is  an  achromatic  lens? 

A.  A  lens  composed  of  two  pieces,  one  of  crown  and  one  of 
flint  glass,  the  first  being  +  and  the  second  — ;  the  latter  one-half  as 
strong  in  refracting  power,  but  of  equal  dispersive  power,  overcomes 
chromatic  aberration. 

Q.     What  is  an  aplanatic  lens? 

A,  It  is  similar  to  the  achromatic  one,  except  that  the  —  lens 
is  divided,  one-half  being  placed  on  either  side  of  the  +  with  the  re- 
result  that  not  only  the  chromatic,  but  the  spherical  aberration  is  over- 
come and  a  fully  corrected  lens  formed.  They  are  used  only  in  high 
power  instruments. 

Q.  To  what  class  of  lenses  does  the  dioptric  system  of  the  eye 
belong? 

A.     To  the  +  class. 

Q.    What  constitutes  the  dioptric  system  of  the  eye? 

A.  The  cornea,  aqueous  humor,  crystalline  lens  and  capsule, 
and  the  vitreous  humor. 

Q.     What  is  meant  by  static  and  dynamic  refraction  of  the  eye? 

A.  Static  means  natural,  and  is  that  condition  which  is  present 
when  the  nerves  and  muscles  of  accommodation  are  at  rest.  Dy- 
namic means  force,  and  is  the  condition  present  when  the  nerves 
and  muscles  are  active. 

Q.    What  is  the  index  of  refraction  of  the  eye? 

A.  Of  the  cornea  and  humors  it  is  about  1.33;  of  the  lens, 
about  1.42.   They  aggregate  in  calculation  so  nearly  the  index  of  glass. 


138  OPTICAL  TRUTHS. 

that  for  practical  purposes,  draw  the  perpendicular  to  the  surface  of 
the  cornea  where  the  incident  ray  strikes  and  calculate  on  the  basis  of 
an  index  of  1.50,  ignoring  the  humors  and  lens. 

Q.  Why  is  the  cornea  necessarily  a  segment  of  a  smaller  sphere 
than  the  globe? 

A.  Because  no  globe  with  an  index  of  refraction  of  less  than 
about  2.00  will  focus  within  its  own  circumference,  hence  the  cornea 
is  of  sharper  curvature  to  bring  the  focus  of  the  dioptric  system 
within  the  eye. 

Q.  Which  meridian  of  the  cornea  has  the  sharpest  curvature  in 
the  normal  eye,  and  why? 

A.  The  vertical,  to  give  the  effect  of  a  +  cylinder  to  act  as  a 
governor  to  the  oblique  muscles. 

Q.     What  is  an  error  of  refraction? 

A,  That  condition  of  the  dioptric  system  in  which  the  retina  is 
situated  in  front  of,  or  behind  the  focus  of  one  or  more  meridians. 

Q.     How  many  kinds  are  there? 

A.     Two,  Hyperopia  and  Myopia. 

Q.     Give  some  symptoms  of  each? 

A.  Of  Hyperopia:  frowning  when  looking  at  distant  objects, 
vertical  wrinkles  on  the  forehead  between  the  eyes,  a  flat  face,  with  low 
nose-bridge,  small  eyes  deeply  set  in  the  head,  small  pupils,  conjunc- 
tivitis, headache,  sick  stomach,  indigestion,  constipation,  piles,  female 
disorders,  almost  all  nervous  alTections,  visions  more  acute  than  |^. 
Of  Myopia:  large,  full  face,  prominent  eye-balls,  high  nose-bridge,, 
large  pupils,  tendency  to  close  the  eyes  when  looking  at  distant  ob- 
jects, inability  to  see  clearly  at  a  distance,  absence  of  hyperopic  symp- 
toms. 


APPENDIX.  139 

Q.     Are  these  symptoms  infallible? 

A.  Oh,  no!  Symptoms  are  only  a  general  guide,  and  may  fail 
completely.     As  a  general  rule  they  are  pretty  reliable. 

Q.     What  is  astigmatism? 

A.  It  is  a  lack  of  spherical  curvature  of  the  cornea,  one  merid- 
ian having  more  convexity  than  the  others,  the  one  at  right-angles  to 
it  having  the  least  amount. 

Q.    In  what  part  of  the  eye  is  it  most  frequently  found? 

A.     In  the  cornea. 

Q.     Where  else? 

A.     Occasionally  in  the  crystalline  lens. 

Q.    Does  it  change  in  amount  ? 

A.  It  does  not  in  the  cornea,  except  in  case  of  injury  or  corneal 
disease.  In  the  lens  it  does,  as  age  affects  the  power  of  accommoda- 
tion. 

Q.     How  many  kinds  of  astigmatism  are  there? 

A.     Seven,  viz:    Normal,  five  kinds  of  regular,  and  irregular. 

Q.     How  may  irregular  astigmatism  be  corrected  sometimes? 

A.  By  using  stenopaic  disks,  or  pin-hole  disks,  either  alone  or 
combined  with  lenses. 

Q.    What  is  a  spasm  of  accommodation? 

A.     It  is  an  involuntary  action  of  the  muscles,  from  nerve  strain. 

Q.     How  many  kinds  are  there? 

A.    Two,  Clonic  and  Tonic. 

Q.     Describe  them  ? 

A.  Clonic  is  an  intermittent  action  foiind  in  almost  all  young 
hyperopes  and  is  overcome  readily  by  fogging.     Tonic  is  a  perma- 


140  OPTICAL  TRUTHS. 

nent  cramp,  is  always  painful,  and  often  requires  atropia  to  subdue  it, 
although  a  pair  of  +  lenses  of  ,50  to  1.00  D  power,  if  worn  con- 
stantly for  a  few  days,  may  conquer  it. 

Q.  How  may  spasm  of  accommodation  affect  the  vision  and 
the  tests  therefor? 

A.  It  may  conceal  a  portion  of  the  amount  of  hyperopia,  may 
make  the  eye  appear  emmetropic,  and  even  cause  it  to  simulate 
myopia,  thus  interfering  with  the  test. 

Q.  What  are  some  special  indications  of  spasm  of  accommo- 
dation ? 

A.  In  testing,  if  patient  sees  better  one  moment  than  another, 
with  the  same  lenses,  it  indicates  clonic,and  pain,  with  reduced  accom- 
modation indicates  tonic  spasm,  showing  that  the  muscle  will  neither 
relax  or  contract  further. 

Q.  What  is  the  difference  between  range  and  amplitude  of  ac- 
commodation ? 

A.  The  range  is  the  difference  between  the  far  point  and  near 
point.  Amplitude  is  the  muscular  effort  required  to  adjust  the  focus 
of  the  eye  to  points  within  that  range. 

Q.  Locate  the  far  points  and  near  points  in  emmetropia,  hyper- 
opia and  myopia? 

A.  The  far  point  in  emmetropia  is  at  infinity,  in  hyperopia  it  is 
beyond,  and  in  myopia  nearer  than  infinity.  The  near  points  in  all 
of  them  are  the  nearest  points  to  which  they  can  accommodate. 

Q.  When  would  you  prescribe  a  spherical,  if  the  test  called  for 
a  compound? 

A.  For  temporary  wear,  if  there  is  some  doubt  about  the  cor- 
rectness of  the  test,  or  for  persons  who  require  a  very  strong  sphere 


APPENDIX.  141 

and  weak  cylinder.  In  the  latter  instance,  because  in  grinding  the 
sphere  all  on  one  side  of  the  lens  the  aberration  thus  caused  would 
counteract  the  benefit  of  the  cylinder. 

Q.  When  would  you  prescribe  a  cylinder  if  the  test  called  for 
compound? 

A.  In  compound  myopia,  or  mixed  astigmatism  where  the  full 
correction  gives  |f  vision,  and  the  sphere  is  —  .50,  or  less,  we  would 
prescribe  only  the  cylinder,  so  long  as  accommodation  remained. 

Q.  When  would  you  prescribe  a  compound  instead  of  a  cyl- 
inder? 

A.  In  simple  myopic  astigmatism,  if  the  cylinder  gave  f  ^  and 
accommodation  is  good  we  put  +  .25  or  +  .50  sphere  in  combina- 
tion, reducing  vision  a  little,  but  assuring  ourselves  we  are  not  over- 
correcting. 

Q.  What  class  of  patients  should  wear  glasses  all  the  time,  and 
why? 

A.  Those  with  an  error  of  refraction.  Hyperopes,  to  relieve 
nerve  strain.     Myopes,  to  improve  vision. 

Q.     Who  should  wear  them  only  for  reading  ? 

A.     Emmetropes  with  presbyopia. 

Q.  Who  may  wear  them  for  distance  but  lay  them  aside  when 
reading? 

A.  Myopes  of  less  than  about  3.00  D.  whose  accommodation  is 
growing  weak. 

Q.  Under  what  circumstances  would  you  prescribe  +  lenses 
for  a  myope? 

A.     If  the  myopia  is  less  than  3.00  D  and  accommodation  is 


142  OPTICAL  TRUTHS. 

gone,  would  give  them  for  reading.  In  simple  myopic  astigmatism 
of  .  50  or  less,  would  give  +  cylinder  axis  reversed. 

Q.     When  would  you  give  —  lenses  to  a  hyperope.? 

A.     Never! 

Q.    What  is  the  greatest  danger  in  prescribing  —  lenses.? 

A.    That  we  will  make  them  too  strong. 

Q.     What  is  most  liable  to  happen  in  prescribing  +  lenses.? 

A.     We  will  not  make  them  strong  enough. 

Q.     How  do  we  calculate  the  nerve  strain  in  emmetropia. 

A.  Add  to  the  amount  of  accommodation  in  the  two  eyes,  the 
amount  of  convergence  which  gives  the  total  strain  per  second,  then 
multiply  by  the  number  of  seconds  devoted  to  near  work  each  day. 

Q.     How  is  the  calculation  made  for  hyperopia? 

A.  Add  to  the  amount  of  hyperopia  in  the  two  eyes  as  much 
more  for  the  strain  involved  through  the  recti  muscles,  and  multiply 
by  the  number  of  seconds  the  patient  is  awake  each  day.  Then  add 
the  strain  of  emmetropia  to  that  and  we  have  the  total  strain  on  the 
hyperope  who  does  not  wear  glasses. 

Q.     How  do  we  calculate  the  strain  in  myopia? 

A.  It  is  only  approximate  in  this  case,  because  of  in-co-ordina- 
ion,  but  it  would  be  safe  to  deduct  the  number  of  dioptres  of  myopia 
from  the  strain  of  the  emmetrope. 

Q.  When  there  are  conflicting  symptoms  in  regard  to  nerve 
strain,  or  to  errors  of  refraction,  in  which  shall  we  place  most  confi- 
dence and  why? 

A.  In  those  which  indicate  nerve  weakness,  or  hyperopia,  be- 
cause we  are  then  on  the  safe  side. 


APPENDIX.  143 

Q.     How  many  kinds  of  muscular  trouble  are  there? 

A.     Two,  cross-eyes  and  muscular  insufficiency. 

Q.     What  is  their  cause? 

A.  The  first  might  be  congenital  or  be  the  etTect  of  accident  or 
disease,  or  hyperopia;  the  second  is  caused  by  errors  of  refraction, 
ninety  per  cent,  of  which  is  hyperopia. 

Q.     How  shall  we  treat  them  ? 

A.  The  first,  by  operation;  the  second  by  correcting  the  errors, 
thus  removing  the  cause. 

Q.     Why  not  use  prisms  for  muscle  trouble? 

A.  Because  it  is  foolish  almost  to  criminality.  If  the  cause  of 
trouble  is  errors  of  refraction,  and  these  are  corrected,  Nature  will  do 
the  rest,  and  prisms  only  interfere  with  her. 

Q.     What  is  the  cause  of  errors  of  refraction  ? 

A.  Over  or  underdevelopment  of  the  eyes  from  improper  nour- 
ishment, either  during  the  period  of  gestation  or  during  the  first  decade 
of  life. 

Q.  Why  do  we  see  things  which  are  not  in  themselves  lumi- 
nous? 

A.     By  the  light  reflected  from  them. 

Q.     What  is  presbyopia? 

A.     Loss  of  accommodation  incident  to  age. 

Q.     Is  it  the  same  in  both  eyes? 

A.     Yes,  because  their  nerve  supply  comes  from  the  same  source. 

Q.     How  much  of  it  can  one  have? 

A.    Three  dioptres. 

Q.  What  is  the  difi'erence  between  presbyopia  and  errors  of  re- 
fraction? 


144  OPTICAL  TRUTHS. 

A.  The  first  is  the  loss  of  a  function,  and  the  second  are  de- 
formities. 

Q.  What  is  the  difference  between  errors  of  refraction  and 
muscular  insutficiencies? 

A.  The  first  are  deformities,  and  the  second  are  weakness  result- 
ing from  those  deformities. 

Q.  If  a  patient  needed  different  glasses  for  far  and  near  work 
but  would  buy  only  one  pair  what  should  you  do? 

A.  Refuse  to  have  anything  to  do  with  the  case  until  patient 
agreed  to  follow  instructions. 

Q.  Does  age  have  any  influence  in  determining  what  to  pre- 
scribe?    If  so  when? 

A.  The  age  itself  has  absolutely  nothing  to  do  with  prescribing. 
The  eiiects  of  age  do,  but  one  person  at  sixty  may  not  need  as  much 
assistance  for  presbyopia  as  another  would  at  forty. 

Q.     What  are  the  principle  obstacles  in  fitting  glasses? 

A.  An  active  accommodation  and  the  idiosyncrasies  of  the 
patient. 

Q.  What  is  the  cause  of  conjunctivitis  and  how  shall  we 
treat  it? 

A.  Hyperopia  is  the  commonest,  a  foreign  substance  under  the 
lid,  infection  or  from  the  use  of  intoxicants,  etc.,  which  interfere 
with  the  circulation.  Treat  by  using  antiseptic  lotions  such  as  salt 
water,  correct  errors  of  refraction  and  order  rest  for  a  few  days. 

Q.  Explain  the  dilference  between  objective  and  subjective  tests; 
which  is  best  and  why? 

A.    Objective  tests  are  those  in  which  the  errors  are  measured 


APPENDIX.  145 

by  reflection  from  the  cornea  or  retina,  and  their  correctness  depends 
much  upon  the  keenness  of  preception  of  the  operator,  with  great 
HabiHty  to  mistakes.  Subjective  tests  are  those  in  which  the  patient's 
preceptive  powers  are  employed  in  determining  the  error,  and  as  he 
has  to  wear  the  correction  it  is  self-evident  it  is  the  best  method. 


GLOSSARY. 

Achromatopsia— Total  color-blindness. 

Albinism— Absence  of  the  layer  of  pigmentum  nigrum  in  choroid. 

Anemia — A  condition  of  wasting. 

Anchylobelpharon— A  stiffening  of  the  eyelids. 

Aneurism — A  wart-like  dilatation  of  vessels. 

Anisometropia— Unequal  vision  in  one's  two  eyes. 

Anopsia — Without  vision. 

Amaurosis — Obscure  vision. 

Amblyopia — See  Amaurosis. 

Ametropia — Imperfect  refractive  condition  of  the  eye. 

Aphakia  — Absence  of  crystalline  lens. 

Arcus  Senilis — Senile  ulcer,  degeneration  of  corneal  cells  forming 

gray  crescent  or  circle  at  edge  of  cornea,  mostly  in  old  people; 

harmless. 
Astigmatism — Without  a  point.    Irregularity  of  the  curvature  of  the 

refracting  media. 
Asthenopia— Fatigue  of  ocular  nerves. 
Atrophy— Loss  of  vitality,  wasting. 

Binocular— Two-fold  vision.    To  see  with  both  eyes  at  once. 
Blepharitis— Inflammation  of  the  eyelids. 
Canthi  (s,  canthus) — Angles  formed  by  the  upper  and  lower  eyelids, 

from  the  middle  to  either  side. 


148  OPTICAL  TRUTHS. 

Catoptrics— Laws  of  reflection  of  light. 

Chalazion— Tumor  of  the  eyehd. 

Chromatopsia — Abnormal  color  sense. 

Cilia- The  eyelashes. 

Ciliary  Body — Apparatus  of  accommodation. 

COLLYRiUM— An  eye-wash. 

COLOBOMA — A  mutilation. 

Conjunctiva — To  join  together.    The  transparent  membrane  which 

lines  the  lids  and  covers  the  front  of  the  eyeball. 
Conjunctivitis— Inflammation  of  conjunctiva. 
CORECTOPIA — Pupil  out  of  place. 
COREDIALYSIS— A  rupture  of  the  iris. 
Cornea — Horny.     The  projection  on  the  front  of  the  globe. 
Cyclitis — Inflammation  of  the  ciliary  body. 
Cycloplegia — Paralysis  of  the  ciliary  muscles. 
Dacryo-cystitis — Inflammation  of  the  lachrymal  sac. 
Daltonism— Color-blindness. 

Dioptre— To  see  through;  a  unit  of  measure  in  optics;  one  metre. 
Diplopia— Double  vision. 
Dynamic — Force. 
ECCHYMOSIS— Black  eye. 
Ectopia — Partial  luxation  of  the  crystalline. 
Ectropion — Eversion  of  eyelids. 

Emmetropia — A  perfect  condition  of  the  refracting  media. 
Embolism— A  rupture. 
Entropion — Inversion  of  eyelids. 
Entozoa— A  wormlike  parasite,  which  finds  its  way  into  almost  any 

portion  of  the  eye,  and  destroys  tissue  by  causing  small  cysts. 


GLOSSARY.  149 

Enucleate — To  remove. 

Epiphora — Overflow  of  tears. 

ESOPHORIA — Insutikiencyof  external  rectus. 

ExoPHORiA — Insufficiency  of  internal  rectus. 

Exophthalmos — Abnormal  prominence  of  eye-balls.  Graves  di- 
sease. 

F1LARIA--A  thread-like  worm  sometmies  found  in  the  cornea. 

Foramen -A  passage  or  opening. 

Fossa— A  ditch. 

Fundus — Bottom. 

Glaucoma — Green;  a  disease  of  the  ciliary  processes  and  optic  nerve. 

Glioma— Glue. 

Hemiopia- Half  vision. 

Hemeralopia— Day  blindness. 

Heterophoria — An  abnormal  muscular  condition. 

Heterophthalmos— Congenital  differences  of  color  in  the  iris,  or  of 
two  eyes. 

HiPPUS— Alternate  contraction  and  expansion  of  pupil. 

HORDEOLUS— A  stye. 

Horopter — The  field  of  vision  included  by  both  eyes  at  once,  with- 
out moving. 

Hyaloid— Glass-like;  a  thin  membrane  which  lines  the  inner  surface 
of  the  eye. 

Hyalitis— Inflammation  of  the  vitreous. 

Hyperphoria— Insufficiency  of  superior  or  inferior  recti  muscles. 

Hypopyon— An  abscess  from  corneal  ulcers. 

INTRA-OCULAR  TENSION— The  degree  of  pressure  from  the  fluids 
within  the  eye. 


ISO  OPTICAL  TRUTHS. 

Iridectomy— A  cutting  of  the  iris. 

IRIDODIALYSIS— Separation  of  iris  from  ciliary  body,  as  a  result  of 

blows. 
IRIDODONESIS— Trembling  of  the  iris. 
Iris  (a  rainbow) — The  colored  portion  of  the  eye  surrounding  the 

pupil. 
Iritis— Inflammation  of  the  iris. 
Keratitis— Inflammation  of  the  cornea. 
Keratokonus— Conical  shape  of  the  cornea. 
Keratonyxis— Puncture  of  the  cornea. 
Leucoma— White. 

Lagophalmos— Inability  to  close  the  lids. 
Locomotor  Ataxia— Creeping  paralysis. 
Macula  Lutea — The  yellow  spot,  or  point  of  sharpest  vision. 
Malingerer — One  who  falsely  pretends  to  have  an  incurable  defect 

of  vision,  or  other  function,  to  excite  sympathy  or  evade  duty. 
Metamorphopsia — Distorted  vision. 
MiGRAiME— Sick  headache. 
MusC/t  VOLiTANTES— Floating  specs  in  the  eye. 
Mydriatics — Drugs  which  suspend  accommodation. 
Myopia— To  close  the  eye. 

Myotics — Drugs  which  stimulate  the  accommodation. 
Nebula— A  cloud. 

Neuritis — Inflammation  of  the  optic  nerve. 
Nictitation — To  wink. 
Nystagmus— A  jerking  of  the  eyeballs. 
Nyctalopia— Night  blindness. 


GLOSSARY.  151 

CEdema — An  exudation. 

Ophthalmia— Inflammation  of  the  eyes. 

Ora  Serrata — Serated  boundary.  The  circle  of  connection  between 
the  retina  and  ciliary  processes. 

Orthophoria — Normal  muscular  condition. 

Ophthalmoplegia  {interna  and  externa) — Paralysis  of  the  sphincter 
muscles  of  pupils  and  ciliary. 

PALPEBRyt  —The  eyelids. 

Pannus — Corneal  vascularization  from  long  continued  irritation. 

Papilla — A  nipple.     The  optic  disk. 

Phakatis  —  Inflammation  of  the  lens. 

Phlyctenule— A  pimple. 

Photophobia — Aversion  to  light. 

Pinguecula — A  small  elevation  on  the  ocular  conjunctiva;  sometimes 
mistaken  for  petrygium. 

Posterior  Synechia— Adheson  of  iris  to  lens. 

Presbyopia— Old  sight. 

Pterygium — A  little  wing.  Is  a  hypertrophy  of  the  conjunctiva 
and  grows  on  sclerotic  and  cornea  sometimes  interfering  with  vi- 
sion.    May  be  removed. 

Ptosis — A  falling  of  the  upper  lid  from  paralysis  of  the  third  nerve. 

Retina— A  net.     Formed  by  expansion  of  the  optic  nerve. 

Sclerotic— Hard.     The  white  of  the  eye. 

Scotoma — Obstruction  of  vision  from  hemorrhages.     Darkness. 

Staphyloma — A  bulging  projection .  Anterior,  comes  after  corneal 
ulcers,  and  is  a  bluish-white  in  appearance.  Posterior,  is  a  pro- 
jecting backward  of  the  posterior  pole  of  the  eye. 


152  OPTICAL  TRUTHS. 

Strabismus— To  squint. 

Stroma -Bedding. 

SUPERCILIUM  —The  eyebrows. 

Symblepharon — Adhesion  of  ocular  and  palpebral  conjunctiva, 
caused  by  escharotics,  such  as  lime,  ashes  or  other  alkalies. 

Synechia— To  hold  together. 

Synchisis— To  flow  together. 

Tapetum— A  carpet. 

Tension— The  condition  of  an  organ  when  under  strain. 

Thrombosis— A  plugging  of  retinal  vessels  by  blood  clots.  Some- 
times causes  hemorrhages  which  bring  at  least  temporary  blind- 
ness. 

Trachoma — (Rough).    Granular  conjunctivitis. 

Trauma — A  wound. 

Tinea  Taksi — Eczema  of  border  of  lids. 

Uvea — A  bunch  of  grapes.     The  choroid,  Iris  and  ciliary  body. 

Vascular — Pertaining  to  vessels. 

Vitreous — Glass-Hke. 

Xanthelasma— Yellow  patches  of  fibrous  tissue  on  the  lids,  mostly 
of  women.     Harmless,  but  may  be  removed. 

Xerophthalmus— Dry  eye. 


McCORMICK 
OPTICAL  COLLEGE 


^      84  ADAMS  STREET        ^ 

*^     ...  CHICAGO  ...     "^ 


Chari.es  McCormick,  M.  D.,  Prest.  Frank  Rumble,  Oph.  D.,  Sec'y 

Professor  of  Ophthalmology.  Professor  of  Mathematics. 

W.  C.  LOAR,  A.  M.,  M.  D.  Almerin  W.  Baer,  M.  D.,  Ph.  G. 

Professor  of  Pathology.  Professor  of  Physiology. 

Wm.  B.  Hunt,  M.  D. 

Surgeon. 


The  Most  Thorough  Course  in 
Optics  in  the  World.  A  Fact 
which  is  attested  by  Hundreds 
of  Graduates  who  are  Success- 
ful Practitioners,  ^.^.^j'.^t^.^ 

A  Post-Graduate  Course  for  Physicians 

A  Course  for  the  Jeweler  and  Druggist 

A  Course  for  Anyone 

who  wants  a  nice  profession. 


PROSPECTUS  FREE  Address,  FRANK  RUMBLE,  Sec'y 


14  DAY  USE 

i  RETURN  TO  DESK  FROM  WHICH  BORROWED 

OPTOMETRY  LIBRARY 


This  book  is  due  on  the  last  date  stamped  below,  or 

on  the  date  to  which  renewed. 

Renewed  books  are  subject  to  immediate  recall. 


i^ 

m 

^ 

m 

K|C 

m 

^ 

W 

i 

M 

W_i 

^ 

Wlk 

K 

«m 

B 

w 

p 

1 

m 

^L 

il^ 

m 

LB21 — 32m — 1,'75 
(S3845L)4970 


General  Library 

University  of  California 

Berkeley 


